"But he who is joined to the Lord becomes one spirit with him." (1 Cor 6:17) It dawned on me after recent studies in 1 Cor that this is alluding to two passages. The first one is Genesis 2:24 - "Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh." The other is actually Deut 10:20 - "You shall fear the Lord your God. You shall serve him and hold fast to him, and by his name you shall swear." It's amazing to see the same imperative "hold fast" used in these two passages. The first talks about the oneness of human marriages, the second with regards to our relationship to God. Paul makes the argument that sexual immorality is more than just sex. We become " one flesh ". The choice is between a prostitute and bizarrely, God Himself.