What happens on the wedding day? Why is this day so special? Of course the surface answer is that a couple is now married and they may live together as husband and wife. But what does this mean in God? Is there more that God wants us to see and understand?
Consider the first wedding: "And the Lord God caused a deep sleep to fall on Adam, and he slept; and He took one of his ribs, and closed up the flesh in its place. Then the rib which the Lord God had taken from man He made into a woman, and He brought her to the man. And Adam said: 'This is now bone of my bones and flesh of my flesh; she shall be called woman, because she was taken out of man.' Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh." (Genesis 2:21-24)
This account may seem very distant from modern customs, but I believe we can find much here to give us direction. In this first marriage, we do not find pomp and ceremony, but only that God brought Eve to Adam and they became "one flesh." If we take the scripture for what it says, we can say very simply that on the wedding day, as a man and woman leave father and mother and cleave unto each other, two become one in God's eyes. The two are so truly one that Adam said Eve was "bone of my bone and flesh of my flesh." Our place is to accept this truth and let it affect every other expression.
When Paul uses this account in Genesis to teach us what God is doing in the church, he uses the same words. If we have been baptized into Christ by the Spirit, we are so one with God that we are "members of His body, of His flesh and of His bones." Paul says this is a tremendous mystery, a mystery once hidden which now has been revealed. God had this mystery in mind when He created marriage as it is. Everything in God's plan works in harmony. The marriage relationship teaches us about Christ and His church, and the church teaches us about the marriage relationship. They are designed by God to work together.
The importance of the wedding day is simply this: it is the culmination of the preparation of the engagement period, and it is the day when the man and woman leave father and mother and their union is begun before God and man. It is not what is said on the wedding day that makes them husband and wife, but what is done: leaving and cleaving. The remainder of their life together is lived on the basis "the two are now one," and this fact must control everything. The order that God has designed for marriage can only work if it is based on the reality that two are now one flesh in God's eyes. If we will always move from this revelation, I believe it will greatly help us to realize God's full purpose in the marriage union.