The natural supremacy of reflection or conscience being thus established; we may from it form a distinct notion of what is meant by human nature, when virtue is said to consist in following it, and vice in deviating from it.
As the idea of a civil constitution implies in it united strength, various subordinations, under one direction, that of the supreme authority; the different strength of each particular member of the society not coming into the idea; whereas, if you leave out the subordination, the union, and the one direction, you destroy and lose it: So reason, several appetites, passions, and affections, prevailing in different degrees of strength; is not that idea or notion of human nature; but that nature consists in these several principles considered as having a natural respect to each other, in the several passions being naturally subordinate to the one superior principle of reflection or conscience. Every bias, instinct, propension within, is a real part of our nature, but not the whole: add to these the superior faculty, whose office it is to adjust, manage, and preside over them, and take in this its natural superiority, and you complete the idea of human nature. And as in civil government the constitution is broken in upon and violated, by power and strength prevailing over authority; so the constitution of man is broken in upon and violated by the lower faculties or principles within prevailing over that, which is in its nature supreme over them all. Thus, when it is said by ancient writers, that tortures and death are not so contrary to human nature as injustice; by this, to be sure, is not meant, that the aversion to the former in mankind is less strong and prevalent than their aversion to the latter: but that the former is only contrary to our nature, considered in a partial view, and which takes in only the lowest part of it, that which we have in common with the brutes; whereas the latter is contrary to our nature, considered in a higher sense, as a system and constitution, contrary to the whole economy of man. 
And from all these things put together, nothing can be more evident, than that, exclusive of revelation, man cannot be considered as a creature left by his Maker to act at random, and live at large up to the extent of his natural power, as passion, humor, wilfulness, happen to carry him; which is the condition brute creatures are in but that, from his make, constitution, or nature, he is the strictest and most proper sense, a law to himself. He hath the rule of right within: what is wanting is only that he honestly attend to it.
The inquiries which have been made by men of leisure after some general rule, the conformity to, or disagreement from which, should denominate our actions good or evil, are in many respects of great service. Yet let any plain, honest man, before he engages in any course of action, ask himself, is this I am going about right, or is it wrong? Is it good, or is it evil? I do not in the least doubt but that this question would be answered agreeably to truth and virtue, by almost any fair man in almost any circumstance. Neither do there appear any cases which look like exceptions to this; but those of superstition, and of partiality to ourselves. Superstition may, perhaps, be somewhat of an exception: but partiality to ourselves is not; this being itself dishonesty. For a man to judge that to be the equitable, the moderate, the right part for him to act, which he would see to be hard, unjust, oppressive in another; this is plain vice, and can proceed only from great unfairness of mind.
But, allowing that mankind hath the rule of right within himself, yet it maybe asked, "What obligations are we under to attend to and follow it?"I answer: it has been proved, that man by his nature is a law to himself, without the particular distinct consideration of the positive sanctions of that law; the rewards and punishments which we feel, and those which, from the light of reason, we have ground to believe are annexed to it. The question then carries its own answer along with it. Your obligation to obey this law, is its being the law of your nature. That your conscience approves of and attests to such a course of action, is itself alone an obligation. Conscience does not only offer itself to show us the way we should walk in, but it. likewise carries its own authority with it, that it is our natural guide, the guide assigned us by the Author of our nature: it therefore belongs to our condition of being: it is our duty to walk in that path, and follow this guide, without looking about to see whether we may not possibly forsake them with impunity.
However, let us hear what is to he said against obeying this law of our nature. And the sum is no more than this: "Why should we be concerned about any thing out of, and beyond ourselves? If we do find within ourselves regards to others, and restraints of we know not how many different kinds; yet these being embarrassments, and hindering us from going the nearest way to our own good, why should we not endeavor to suppress and get over them?"
Thus, people go on with words, which, when applied to human nature, and the condition in which it is placed in. this world, have really no meaning. For does not all his kind of talk go upon supposition, that our happiness in this world consists in somewhat quite distinct from regards to others, and that it is the privilege of vice to be without restraint or confinement? Whereas, on the contrary, the enjoyments; in a manner all the common enjoyments of life, even the pleasures of vice, depend upon these regards of one kind or another to our fellow creatures. Throw off all regards to others, and we should be quite indifferent to infamy and honor: there could be no such thing at all as ambition, and scarce any such thing as covetousness; for we should likewise be equally indifferent to the disgrace of, poverty, the several neglects and kinds of contempt which accompany this state; and to the reputation of riches, the regard and respect they usually procure. Neither is restraint by any means peculiar to one course of life; but our very nature, exclusive of conscience, and our condition, lays us under an absolute necessity of it. We cannot gain any end whatever without being confined to the proper means, which is often the most painful and uneasy confinement. And, in numberless instances, a present appetite cannot be gratified without such apparent and immediate ruin and misery, that the most dissolute man in the world chooses to forego the pleasure, rather than endure the pain.
Is the meaning, then, to indulge those regards to our fellow-creatures, and submit to those restraints; which upon the whole, are attended with more satisfaction than uneasiness, and get over only those which bring more uneasiness and inconvenience than satisfaction? "Doubtless this was our meaning." You have changed sides then. - Keep to this: Be consistent with yourselves; and you and the men of virtue are, in general, perfectly agreed. But let us take care, and avoid mistakes. Let it not be taken for granted, that the temper of envy, rage, resentment, yields greater delight than meekness, forgiveness, compassion, and good-will: especially when it is acknowledged, that rage, envy, resentment, are in themselves mere misery; and the satisfaction arising from the indulgence of them is little more than relief from that misery; whereas the temper of compassion and benevolence is itself delightful; and the indulgence of it, by doing good, affords new positive delight and enjoyment. Let it not be taken for granted, that the satisfaction arising from the reputation of riches and power, however obtained, and from the respect paid to the them is greater than the satisfaction arising from the reputation of justice, honesty, charity, and the esteem which is universally acknowledged to be their due. And if it be doubtful which of these satisfactions is the greatest, as there are persons who think neither of them very considerable, yet there can be no doubt concerning ambition and covetousness, virtue and a good mind, considered in themselves, and as leading to different courses of life; there can, I say, be no doubt, which temper and which course is attended with most peace and tranquillity of mind; which, with most perplexity, vexation, and inconvenience. And both the virtues and vices which have been now mentioned, do in a manner equally imply in them regards of one kind or another to our fellow creatures. And with respect to restraint and confinement: whoever will consider the restraints from fear and shame, the dissimulation, mean arts of concealment, servile compliances, one or other of which belong to almost every course of vice, will soon be convinced, that the man of virtue is by no means upon a disadvantage in this respect. How many instances are there, in which men feel, and own, and cry aloud under the chains of vice with which they are enthralled, and which yet they will not, shake off? How many instances, in which persons manifestly go through more pain and self-denial to gratify a vicious passion, than would have been necessary to the conquest of it? To this is to be added, that when virtue is become habitual, when the temper of it is acquired, what was before confinement ceases to be so, by becoming choice and delight. Whatever restraint and guard upon ourselves may be needful to unlearn any unnatural distortion or odd gesture; yet, in all propriety of speech, natural behaviour must be the most easy and unrestrained. It is manifest, that in the common course of life there is seldom any inconsistency between our duty and what is called interest. It is much seldomer that there is an inconsistency between duty and what is really our present interest; meaning by interest, happiness and satisfaction. Self-love, then, though confined to the interest of the present world, does in general perfectly coincide with virtue, and leads us to one and the same course of life. But, whatever exceptions there are to this, which are much fewer than they are commonly thought, all shall be set right at the final distribution of things. It is a manifest absurdity to suppose evil prevailing finally over good, under the conduct and administration of a perfect mind.
The whole argument which I have been now insisting upon, may be thus summed up and given you in one view. The nature of man is adapted to some course action or other. Upon comparing some actions with this nature, they appear suitable and correspondent to it: From comparison of other actions with the same nature there arises to our view some unsuitableness or disproportion. The correspondence of actions to the nature of the agent renders them natural; their disproportion to it, unnatural. That an action is correspondent to the nature of the agent, does not arise from its being agreeable to the principle which happens to be the strongest; for it may be so, and yet be quite disproportionate to the nature of the agent. The correspondence, therefore, disproportion, arises from somewhat else. This can be nothing but a difference in nature and kind, (altogether distinct from strength) between the inward principles. Some, then, are in nature and kind superior to others. And the correspondence arises from the action being conformable to the higher principle; and the unsuitableness from its being contrary to it. Reasonable self-love and conscience are the chief or superior principles in this nature of man: because an action may be suitable to this nature, though all other principles be violated; but becomes unsuitable, if either of those are. Conscience and self-love, if we understand our true happiness, always lead us the same way. - Duty and interest are perfectly coincident; for the most part in this world, but entirely and in every instance, if we take in the future and the whole; this being implied in the notion of a good and perfect administration of things. Thus, they who have been so wise in their generation, as to regard only their own supposed interest, at the expense and to the injury of others, shall at last find, that he who has given up all the advantages of the present world, rather than violate his conscience and the relations of life, has infinitely better provided for himself, and secured his own interest and happiness.
 Every man, in his physical nature, is one individual single agent. He has likewise properties and principles, each of which may be considered separately, and without regard to the respects which they have to each other. Neither of these are the nature we are taking a view of. But it is the inward frame of man, considered as a system or constitution: whose several parts are united, not by a physical principle if individuation, but by the respects they have to each other; the chief of which is the subjection which the appetites, passions, and particular affections, have to the one supreme principle of reflection or conscience. The system or constitution is formed by and consists in these respects and this subjection. Thus, the body is a system or constitution; so is a tree; so is every machine. Consider all the several parts of a tree, without the natural respects they have to each other, and you have not at all the idea of a tree; but add these respects, and this gives you the idea. The body may be impaired by sickness, a tree may decay, a machine be out of order, and yet the system and constitution of them not totally dissolved. There is plainly somewhat which answers to all this in the moral constitution of man. Whoever will consider his own nature, will see, that the several appetites, passions, and particular affections, have different respects amongst themselves, They are restraints upon, and are in a proportion to, each other. This proportion is just and perfect, when all those under principles are perfectly coincident with conscience, so far as their nature permits, and, in all cases, under its absolute and entire direction. The least excess or defect, the least alteration of the due proportions amongst themselves, or of their coincidence with conscience, though not proceeding into action, is some degree of disorder in the moral constitution. But perfection, though plainly intelligible and supposable, was never attained by any man. If the higher principle of reflection maintains its place, and, as much as it can, corrects that disorder, and hinders it from breaking out into action, this is all that can be expected in such a creature as man. And though the appetites and passions have not their exact due proportion to each other; though they often strive for mastery with judgment or reflection; yet, since the superiority of this principle to all others is the chief respect which forms the constitution, or so far as this superiority is maintained, the character, the man, is good, worthy, virtuous.