Luther On Trinity 22

Do Christians still sin? Yes. But do they hate their sin? Yes. And they want to be rid of it. The person who loves his sin, who persists in it, cannot be considered a Christian.

Luther:

We also hear about this wicked servant that, after he had experienced grace at the hand of the king, he became proud and obstinate, stirring up the king's wrath once more. That's the way the godless world is which horribly misuses this doctrine of the forgiveness of sins. Some refuse to admit their sins; even though they are wallowing in sin over their heads, yet they refuse to admit that they are sinners. For such people there is not forgiveness; for as we said earlier, If there is no sin, neither can there be any forgiveness. Some keep right on sinning after receiving forgiveness, believing that the gospel allows everyone to do just as he pleases. But the gospel is a message for the depressed, for the people with a guilty conscience, not for those who keep on defensing their sins, nor is it for those who deliberately sin against a gracious God.