The Bible says homosexuality is a sin so how can a gay lay pastor use the Bible to preach?

I was tossing out some old newspapers the other day and my eye caught a story about a local Christian church that sanctioned a gay lay pastor, my thought, with out laying value or anything on the lay pastor, was how can someone who is homosexual which the Bible clearly states as sin teach a congregation from it? In other words how can a gay pastor teach someone against something he is doing? That would be like a pastor trying to teach and preach against adultery when he has a wife and 2 other g/f. I can’t see how it can be done. With out getting into the Bible being a fake fairy tail book or God a myth focusing just on how a gay pastor can preach and feed a congregation about a sin (as the Bible say it is) how do you figure that can be done if at all?