(Mat 19:4-6) "And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female, and said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh? Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder."

This verse is simply about marriage, not crazy gnostic insanity that you read on a wall of a bathroom in a mental institution. Paul explains the meaning well enough in 1 Cor 6:16 "What? know ye not that he which is joined to an harlot is one body? for two, saith he, shall be one flesh." I don't think it could be any clearer what he means. The consumation of a marriage makes a man and a woman one flesh. Also, Paul explains divorce well enough when he says Rom 7:3 "So then if, while her husband liveth, she be married to another man, she shall be called an adulteress: but if her husband be dead, she is free from that law; so that she is no adulteress, though she be married to another man." The Law says that a woman is free from her husband when he dies and a man is free from his wife when she dies. When Jesus says (Mat 19:9), therefore, that a man can divorce his wife for the cause of fornication only and marry another, he is saying that in the case of a Scriptural divorce the guilty part is viewed as being dead thus making the innocent party free to remarry. After all, under the Law of Moses, the one who committed adultery would have been stoned to death. Therefore, in the New Testament, since we don't have stoning, divorce is allowed as if the person had been stoned to death.