So say Anthony Esolen and S. M Hutchens:
The basis of that belief is exemplified in St. Paul's assurance to the Corinthian church that what some of its believers used to be—and here he recited a catalog of sins that included arsenokoitai ("sexual perverts") — they no longer were, because they had been washed, sanctified, and justified in the name of the Lord Jesus Christ and the Spirit of our God.
Later they spell this out, pointing out that this does not mean Christians never sin:
Let us be especially careful here, to obviate misunderstanding. Referring to our lives in time, and in a spirit of mortification, we may say, with St. Peter, "I am a wicked man."We may say, "I am a thief," "I am a harlot," "I am a liar," meaning that I have committed these sins, they weigh upon my shoulders, they are the splinters of my self-hewn cross, which I bear under my flesh. We say so in shame. But we do not thereby express an ultimate or God-ordained identity. Quite the contrary. We mean, "This is what I am in a distorted sense, because of what I have done, and because of the evil that I am still fearfully tempted to do."
Thus they helpfully conclude:
There are Christians who are thieves, because there are Christians who are sinners. But there can be no such thing as a Christian thief. We are ourselves at last when we can say, in glory, "It is not I, but Christ who lives in me." And Christ is no sinner.Lots there to think and pray about...