1 John 2:1-6. (NIV)
1My dear children, I write this to you so that you will not sin. But if anybody does sin, we have one who speaks to the Father in our defense – Jesus Christ, the Righteous One. 2He is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world.
3We know that we have come to know him if we obey his commands. 4The man who says, “I know him,” but does not do what he commands is a liar, and the truth is not in him. 5But if anyone obeys his word, God’s love is truly made complete in him. This is how we know we are in him: 6Whoever claims to live in him must walk as Jesus did.
The person who does not obey Christ’s commands is equated here with the one walking in darkness in v. 6 of the previous chapter. We walk in light by obeying God, and when we do, his love is made complete in us and we have fellowship with each other just as we do with the Father and the Son. Unity in Christ comes not from correct doctrine, but from obeying God’s commands and thereby letting his love shine in us. And when I desire to do this but fail, Jesus is the atoning sacrifice for my sins, so that I may be forgiven and purified of all sin.
This is the exact opposite of “easy believism” John clearly says that if I am in Christ, I will live as Christ lived. Sanctification – becoming like Jesus – is not optional.