A childhood belief about oral sex

I thought that oral sex was making out. I thought this until I was 20 and was sitting in a sermon about sex before marriage and the pastor speaking to us condemned oral sex even in marriage. I didn't understand what was wrong with making out. He then said just because the plumbing fits doesn’t mean God intended it that way. Later that night I figured out what oral sex really was. I think this guys sermon caused more people to have dirty thoughts than it prevented.