Sin is one of those things that we don't like to talk about anymore in the Body of Christ, but it is a real thing.
4 Everyone who sins is breaking God’s law, for all sin is contrary to the law of God. 5 And you know that Jesus came to take away our sins, and there is no sin in him. 6 Anyone who continues to live in him will not sin. But anyone who keeps on sinning does not know him or understand who he is. (1 John 3:4-6, NLT)
This passage is so clear. Sin is that which goes against the law of God. Sin goes against love (as defined by God), against righteousness and against holiness. It is to live as we please as opposed to the way that pleases God.
Jesus died so that the penalty of our sin might be paid for. In Him there is no sin; therefore, when we continue to live in Him (in obedience), we too will live a life that pleases God. As believers, we do not practice or continue in sin because we know Him and understand (by faith) who He is.