“‘If a man has sexual relations with a man as one does with a woman, both of them have done what is detestable. They are to be put to death; their blood will be on their own heads.

It’s right between having sex with your daughter in law (same punishment) and marrying both a woman and her mother (punishable specifically by burning).

Why some Christians take it seriously? I don’t know. They seem to be very selective about which Jewish laws to keep, and how. And they totally ignore Jesus’ teachings on such things, which seems odd that Christians would follow Mosaic laws to the letter instead of following Jesus’ interpretation. That’s what a Jewish Pharisee would do, not a follower of Jesus.