This passage tells us a great deal about God’s design for marriage. We are to leave our parents and “be united” to each other. The two are to become one flesh. God’s design for marriage is a one-flesh union. The word for flesh in the OT where this passage originated can be translated as “person.” For example, it says, “I will pour out my spirit on all flesh.” That means people. So, Jesus is saying that marriage is two people becoming one person, one organism. It’s no longer two people. It is one person.