Genesis frequently uses a pattern or theme of return to the initial state. For example, [Genesis 3:19 states,](https://www.biblegateway.com/passage/?search=Genesis+3%3A19&version=NET)

>By the sweat of your brow you will eat food until you return to the ground,
for out of it you were taken; for you are dust, and to dust you will return.”

In the story of Noah, God returns to the [beginning state of creation](https://www.biblegateway.com/passage/?search=Genesis+1%3A2&version=NET) (the waters) by flooding the earth and the rest of The Bible is centered on returning man to the state before the fall vis-a-vis the sacrifice of Jesus, so this is both a Macro theme and a Micro theme.

The statement than man and woman will be one flesh appears to be another example of that theme of returning to the initial state. It is not that Adam and Eve are becoming one flesh, but that they are becoming one flesh *again*.

[This interpretation is largely dependent on the specifics of the creation of Eve.](https://www.biblegateway.com/passage/?search=Genesis+2%3A18-25&version=NET) Many scholars believe that Adam was initially crated as [possessing both male and female aspects](http://www.amazon.com/dp/0830828346/?tag=stackoverfl08-20). This is not the same as androgynous, but instead Adam was dual-gendered, both fully male and female until the creation of Eve. According to this school of thought, the word ["rib"](https://hermeneutics.stackexchange.com/questions/20122/is-the-translation-rib-for-the-hebrew-%D7%A6%D6%B5%D7%9C%D6%B8%D7%A2-tsela-in-genesis-222-justifie/20131#20131) would be better translated as "side" or "side chamber" and when God created Eve he took a part of the man's side chamber with which to create eve. In other words, god literally took a part of Adam - the female part - and used it to create Eve.

If this is the case, then Adam and Eve are becoming one flesh again through marriage and without Eve, Adam is literally missing a peice of his soul. By becoming one flesh Adam and Eve return to the initial state of creation - the way God meant for man to be, yet mankind is no longer alone. Through marriage that peice of Adam that was taken from him is returned to him and Adam and Eve are again "one flesh".