Christians must not think they can continue sinning with impunity. Sin is utterly inappropriate in the life of a Christian. It is incompatible with the concept of repentance. A person cannot change his/her ways but continue going the same way. It is not logically, or practically, possible.
But the Bible is much more explicit than that on this issue.
Paul addressed this suggestion in Romans 6. There the argument was that since, as sin has increased, God’s grace has increased even more, sinning must be a good thing. It increases grace. If I sin more I will experience more of God’s grace. Most people will see that as a rather strange argument but there will always be people looking for excuses to continue sinning.
Paul’s response was “By no means!” (Romans 6:2). That response is repeated in 6:15 after another rationale for sin has been posited. There the argument is that Christians are not under the law and so must be able to sin. Again, Paul cries out “By no means!”
Paul’s reasons have to do with the change that has happened in a Christian’s life at the point of baptism. It is somewhat mystical and difficult to understand but the biblical truth is that when a believer is baptised, he/she is somehow included in Jesus’ death. In fact, the baptism is a representation of dying and rising again to a new life. Christians have actually died and been raised again to a new life – obviously not physically but spiritually and really.
The old person was a slave to sin. The unbeliever cannot not sin. He/she is a slave. But the Christian can not sin because he/she, having died, is no longer under the power of sin. He/she is to believe that he/she is now dead to sin and alive to God (Romans 6:11) and therefore is not to let sin reign in his/her body (6:12) but offer him/herself to God to serve righteousness (6:13).
The Christian has turned his/her back on sin (repentance) and there has been a spiritual transaction that means that that person is no longer simply a slave and compelled to sin, but is free and can claim that freedom so as to not sin.
None of this implies that Christians are perfect in not sinning. There is a still a battle to be waged with sin. It is simply to say a) that it is possible to not sin and b) that Christians should never believe they can continue sinning.
When non-Christians sin it is simply because they have no choice. They are slaves to sin. They might choose, on some occasions, not to sin but more generally, they simply cannot escape sin – until this dying and rising with Christ is a reality in their lives.
When Christians sin it is not because they were compelled to but because they chose to. Christians have the freedom to say “No”. When they say “Yes” to sin, it is because they have chosen not to say “No”. Christians therefore must take responsibility for their choices and seek forgiveness.
When they do, God faithfully, lovingly and mercifully forgives.
1 John 1:9
If we confess our sins, He is faithful and just and will forgive us our sins and purify us from all unrighteousness.