A Red Letter Christian is a person who belongs to a group that seeks to weight the Scriptures, making some more important than others. Red Letter Christians say that the words written in red (and thus said by Christ) carry more spiritual weight than the other words in the Bible.
There is a whole host of hocus pocus emanating from this current movement (which I have studied very little, so I can’t speak authoritatively to many of their beliefs except one). One well-known statement they have made is, since Jesus never addressed homosexuality directly, He didn’t condemn it. They state that later condemnations of homosexual behavior by Paul were somehow tainted by being too far removed from Christ.
See what I just did there? Showed you how a group that wishes to welcome gay people to their church without requiring them to repent of sin (like anyone else must) ends up justifying their decision by claiming that some parts of Scripture are tainted or not altogether important.
To recap: all of Scripture is one, and totally unified. Jesus did speak of marriage in Matthew 19:4-6. He specifically stated that it was to be between a male and a female, according to God’s design in creation, and that it was to last as long as natural life (that divorce was only allowed by Moses due to the hardness of human hearts).
All Scripture is God-breathed. If we treat any of it as extraneous, we do violence to all of it and to its unity. (I say this in love to my fellow Baptists who make fun of the genealogies. God put them there for a reason, too. He wasn’t up late one night with insomnia when He inspired them . . .).
Be aware of the Red Letter Christians. You may have to do damage control for them after they have messed with a new Christian’s mind.