The modern idea of “being one flesh” is that a couple is two separate individuals who lead separate lives but because they live together under one roof and have sex once in awhile they are one flesh. They are independant people most of the time but dependent on each other at certain times. Biblically this is not the case.
In Genesis 2: 23-24 it says,
This is now bone of my bones, and flesh of my flesh; she shall be called woman for she was taken out of man.’ That is why a man leaves his father and mother and is united to his wife, and they become one flesh.
The idea is that man and woman are created for each other and, when united in marriage, are no longer two separate people but one flesh. In Ephesians 5 Paul admits that “this is a profound mystery” but encourages men to love their wives as they love their own bodies. “In the same way, husbands ought to love their wives as their own bodies. He who loves his wife loves himself. After all, no one ever hated his own body, but they feed and care for their body, just as Christ does the church” (Ephesians 5: 28-30)
When we are single we are selfish in our desires, actions and behaviours. I’m not referring to negative selfishness but just the simple selfishness of putting yourself first. When we get married we have to think of the other person as part of our own flesh and therefore care and nourish them in the same manner we cared and nourished ourselves when we were single.
A healthy individual will exercise, take care of themselves, gauge their emotional state and strive for improvement. This shouldn’t stop when you get married as you are simply adding to your own self. You are not adding a competitor to your life but a completor. A healthy marriage should be seen as an individual organism. This doesn’t mean that you lose your identity to the other or cease to be an individual. Take the image of two hands with their fingers interlocked. You can clearly see the differences between the two hands but together they form a stronger entity.
Being one flesh is being all consumed with the other person as a single person can be all consumed with themselves. It is not an unhealthy, obsessive consuming, rather it is thinking of the other’s benefit more than your own, because as one flesh, when you put the other first you are actually benefiting yourself. Being one flesh is being interdependent. It’s knowing that you’re better and stronger together. You are completing each other and thereby completing yourself.