Marriage is the coming together of two different individuals from different background in order to form a solid union. To achieve this solemnity, these two person must have a concrete agreement.
Marriage in itself is an institution where you can never graduate from. It has a way of biding or joining two different families, nations with different culture together in order to pursue the same goal. You don't just jump into marriage, you must have gather enough information from those who have been into it so that you will be able to handle it with all wisdom and maturity. That is why before embarking on this journey, the two couples must have been into relationship for some years so as to enable them study and understand themselves very well.
God in his wisdom deliberately used marriage to bring unity to his people; in Genesis chapter 2 verse 24 "therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh; this is a mystery indeed, two becoming one. It is so because God sees things differently from the way man sees it. Mathematically, it is expect that 1+1 should become two. But the wisdom of God which supersede the wisdom of man has made it possible that when you add two different persons together, which must be a male and a female it becomes one. He made it possible this way so that there will be an everlasting and solid love between them, and even establish a strong relationship and unity with both family.