There are an overwhelming number of atrocities that have been committed by those who claim to be Christians, those who claim to be acting in the name of the Son. I have seen modern nazis claiming that their actions are in the name of Christ. Many money-grubbers are leaders of some of the largest Christian churches in the world. Usually when confronted with immorality from those who claim to be Christians, we will say, “well they are not a true Christian.” But this raises the question of the behavior of a true Christian. So then, does a true Christian sin?
We see this sort of answer all of the time, and on some level, it does matter. Now it does not matter insofar as the truth of Christian belief is concerned. Even if Adolf Hitler were a Christian, that would say absolutely nothing about whether Christianity was true. 
It would only be said that some very immoral people have claimed to be Christians. That certainly is the case, there are, and have been, many immoral people who claim to be Christians. But a negative social affect says absolutely nothing about whether this system is true. So if we are asking ourselves whether Christian belief is really the truth, the absolute last place we should look is at the most extreme examples (in fact there are people on the other extreme doing very good things for the world).
This question only matters when we attempt to discover what our behavior, as Christians, should be. When people ask whether a Christian can continue in sin, or when people try to find justification for their sins, we wonder whether these are true Christians, and we ask, does a true Christian sin? Questions such as this arise from our observation of human nature and the nature of our salvation. They are not new, and were even addressed by Paul, and Christ himself.
Does A True Christian Sin? Yes.
Jesus told the parable of the tax collector and the Pharisee (Luke 18:9-14). The Pharisee proudly went into the Temple, praying to God, “I thank you that I am not like other men. I am not a sinner. I fast and I pay the alms. I am a good person.” But the tax collector felt unworthy to be in God’s Temple, beating his chest, he said, “God, have mercy on me, a sinner!” Jesus said that it was the tax collector who received mercy, and the Pharisee left unjustified. The person who claims to be without sin is a liar (1 John 1:8).
Therefore, of course a true Christian sins, because everybody sins. As Doctor Frank Turek pointed out, “I am a hypocrite. When people tell me that they cannot go to church because of all of the hypocrites down there, I say, ‘come on down, pal, we have room for one more.’ The church is a hospital for sinners, not a country club for saints. I will never be perfect. That is why Christ had to come.” Thus, Jesus said, “It is not the healthy who need a doctor, but the sick. I have come not to call those who think they are righteous, but those who know they are sinners into repentance. For go and learn what this means: ‘I desire mercy, not sacrifice.'” (Matthew 9:11-12).
Those of us who try to claim that we are righteous are liars, and cannot be justified before God, because our own righteousness always falls short (Romans 3:23). Most religious systems teach that good people are brought to God after death, and bad people are brought to punishment after death. Well, that is true. The problem, though, is that nobody is good. We are all sinners. Does a true Christian sin? Yes. Everybody does.
Does A True Christian Sin? Yes. But We Strive Against It
So, we are all sinners, and all headed for Hell. But Christ absorbed the punishment that each of us deserves; he took the wrath of God on himself so that we would not have to. With that in mind, the question sometimes arises about why we even try to do righteousness. Christ died for our sins, so why not just sin freely and without guilt? Well, the answer is that when we have been saved, we have been born again (John 3:3).
That is to say that we have literally become new creatures, as a supernatural work of God (2 Corinthians 5:17). As such, we are being guided by the Holy Spirit, on the narrow way that leads to life (Hebrews 12:8-10). It is such that we feel as though we cannot sin, or that we must strive against sin. We love God too much to sin. It is as though we were in a relationship with a spouse, and while we have the capacity to cheat on them, we love them too much to do that. So the same with our relationship with God. We love him too much to have the desire to sin against him. While we do still sin, it nauseates us because we have violated God’s law.
When it is said that we have become new creatures, or be born again, that is to say that the person we once were was crucified with Christ. That person is dead (Romans 6:6). Therefore, we are to count ourselves as dead to sin, and alive to Christ (Romans 6:11). Every desire that our flesh has is something that we know must be rebelled against (Romans 6:12). Therefore, rather than offering ourselves as instruments of sin, we instead offer ourselves to God (Romans 6:13), mastered and following only the grace of the Lord (Romans 6:14).
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