Clarity

Darrell Bock is a well known Biblical scholar, and a professor at Dallas Theological Seminary. He's written a Biblical response to same sex marriage. Same sex marriage supporters often try to argue that the Bible condones polygamy, incest, and other variants on monogamous marriage. I find the dismantling of this argument particularly helpful. Where the Bible talks about these things, it is clear from the context that it is descriptive, and not prescriptive.

You also often hear, sometimes from Christians, that the Old Testament prohibitions on homosexuality are just like the ceremonial laws that the ancient Israelites had to observe, with dietary restrictions, and restrictions on wearing clothing made of different fabrics. These Old Testament laws no longer apply.

Careful hermeneutics will help you to understand that the ceremonial laws served a purpose that is no longer needed, because they were abrogated by Christ. The moral laws remain. Like it or not, any expression of sexuality outside of monogamous, opposite sex marriage is a sin in the eyes of God.

http://www.thegospelcoalition.org/article/bible-same-sex-marriage-6-wrong-trajectories