Therefore a man shall leave his father

.... and mother and cleave (be joined) to his wife, and they shall become one flesh (Genesis 2:24).   “Therefore” connects to verse 23 “She is bone of my bone ....  because she was taken out of man  (verse 23). God formed Eve out of Adam's rib, and the picture being painted here,  is that marriage joins them back together in an indivisible bond (one flesh).  Being made in the image of God,  we are body soul and spirit. And all of us,  at some level,  have violated the ideal being presented here.

God formed the woman from the man, and if we are to follow God's ideal for marriage,  God needs to do the joining, and done His way.  Made in the image of God, we are body, soul and spirit. Unbelievers are dead in trespasses and sins (Ephesians 2:1), so the spiritual component of the joining of believer with unbeliever is impossible.  It's forbidden for the Christian (2 Corinthians 6:14).  God's perfect plan is that we be joined in body, soul and spirit.  It's counter cultural,  in that the Word sees no connection between sexual, soulish and spiritual intimacy. But sex is better when we do it God's way. After all it was His idea, and He knows how best to do it!

The order leave, cleave, one flesh is important. Leaving is much more than physical. If we don't leave in an emotionally healthy way  (either by not having grown up, or by bitterness), we will not be able to cleave (adhere to each other) well.  It will also diminish the sex. It is said that the relationship you have with the worst of your parents will be the same you have with your spouse,  six months after you get married (Hebrews 15:12). Being joined by God has to do with covenant and community, and in healthy societies community helps in the cleaving when it gets difficult (when not if!). Jordan Peterson comments we need covenant, because “You're trouble and I'm trouble.” It's only through covenant commitment to work through the difficulties,  that marriage can survive.

Corresponding to the three Greek words all translated “love,” in English, there's a trilogy of ways we are instructed to love one another in marriage.  A little over simplistically,  the highest love is agape love.  It's the  unconditional love with which God so loved the World,  that He sent His son at incredible cost to save us. Then there is phileo love (Philadelphia is the city of brotherly – delphos – love). It's affectionate,  friendship love. Finally there is eros.  We get our word erotic from this,  and for our purposes we can think of it as sexual love.  The order leave, cleave, one flesh is important because, for one thing if we engage in eros before we have properly bonded in phileo,  our friendship love will be stunted, and when “the music fades,” we'll have nothing to fall back on

Father, in many things we all fail (James 3:2), and my first thought here is “Lord have mercy upon us.” There is forgiveness, restoration  and healing of course, but this is costly both to You  (the cross) and to us in that we need to work through the issues, and in breaking free from the power and polluting influence of our sin (sanctification).  And there are always issues (Exodus 20:5 again), and we only break free as we continue in, and obey Your Word (John 8: 31, 32). We need Your help and Your mercy in Jesus Name Amen