First John 2:1 could be translated: "These things write I unto you that ye do not commit a single act of sin." John was not dealing with habitual sin but with single acts of sin. This is a high standard, and you may wonder if it is possible for a child of God to successfully live this way. We need to realize what Christ has actually done for us.
In the light of our experience, however, this may well cause us to despair, for we realize that we do commit acts of sin. The next phrase in 1 John 2:1 says, "And if any man sin, we have an advocate with the Father, Jesus Christ the righteous." When we do commit an act of sin and Satan would accuse us before the Father, there is no way he can reach us because we stand before God in the righteousness of Christ, "even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference" (Rom. 3:22). So Jesus has become our righteousness, and He stands in the presence of God on our behalf.
"Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us" (Rom. 8:34).