Christians arn't perfect, we still sin. In fact the bible says that whoever claims they have no sin is a self deceived liar. (1 John 1:8)
But there is a radical spiritual difference between a Christian and a lost person in regards to sin. The main difference is that even though sin is present in both persons, the Christian has the ability to say no to sin and put it to death because of the work God has done in his life:
1. Jesus not only saves from the penalty of sin, but from sin as a whole, which includes the power and dominion of sin,
2. the Holy Spirit has been given to the Christian to put sin to death (Romans 8:13)
3. the Christian is a new creation who's general pattern of thought and desire is for righteousness (2 Corinthians 5:17, Matthew 5:6)
But when Christians sin, things get messy. Sin defiles our conscience, even though we don't switch back and forth between saved and lost when we sin, our defiled conscience makes us loss assurance that we are saved, and feel as though we are lost because sin has clouded our view of Christ and broken fellowship with him.
There are usually 2 ways people deal with committed sin, either pretend it's ok and try harder not to do it, or acknowledge it's an evil committed against God and trusts that if we confess our sins, God will forgive us and cleanse us (1 John 1:9).
What's even more messy is that for a season, Christians can act like a lost man trying to clean himself by teeth gritting effort to not sin instead of confessing he has wronged God(The case of David after committing adultery with Bathsheba.).
I guess the lesson here is to really know what the bible says about the work God does in a person's soul in salvation, so that we benefit ourselves by
1. being humbled because of the presence of sin, to trust in God for victory over them and not to the flesh
2. not suffering from unnecessary guilt by believing in a standard for Christian different from the bible
3. not being deceived by false assurance, thinking we are saved when sin still has dominion over us.
and we benefit others by
1. not making a hasty judgment regarding the state of their soul when someone confesses sin to us,
2. knowing how to give truthful and loving counsel that are appropriate for the specific situation
Left to ourselves we are desolate, but the Lord is constant help to those who trust Him.
