Monogamy, polygamy, and divorce

But I say to you that everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery, and whoever marries a divorced woman commits adultery (Mt 5:32). 

3 And Pharisees came up to him and tested him by asking, “Is it lawful to divorce one's wife for any cause?” 4 He answered, “Have you not read that he who created them from the beginning made them male and female, 5 and said, ‘Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh’? 6 So they are no longer two but one flesh. What therefore God has joined together, let not man separate.” 7 They said to him, “Why then did Moses command one to give a certificate of divorce and to send her away?” 8 He said to them, “Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so. 9 And I say to you: whoever divorces his wife, except for sexual immorality, and marries another, commits adultery” 10 The disciples said to him, “If such is the case of a man with his wife, it is better not to marry.”(Mt 19:3-9).

i) Catholic apologists, defending the indissolubility of marriage, argue that the porneia-clauses mean something other than adultery as a justification for divorce. One argument is that Matthew doesn't use the specific word for adultery.

They also contend that the reaction of the disciples indicates a more radical position than adultery as a justification for divorce, since that was already a conventional viewpoint in Judaism. So Jesus must be saying something different. 

ii) I think Matthew uses porneia to include adultery without excluding other sexual sins. Adultery would be the most common cause of marital dissolution. That's the default justification. But in the context of the Roman Empire, there were other sexual sins, especially among pagan Gentiles, that come into play. So Matthew uses a broader word to cover adultery without restricting the grounds to adultery.

iii) Whatever else porneia may mean or not mean, it doesn't mean annulment. 

iv) Since the grounds for annulment are not only broader than adultery, but broader than sexual sin generally, if the Catholic interpretation is correct, then the disciples have little to fear, since the "new" policy is even more liberal as the old policy of Hillel. In practical, it's the functional equivalent of a very lax divorce policy. Annulment is a loophole far larger than adultery. Catholic apologists chafe at the comparison with divorce, but their distinction is sophistical. 

v) It may be that the reaction of the disciples has less to do with what Jesus says about narrow grounds for divorce than his implicit position on monogamy. In Jewish practice, a husband didn't have to divorce his wife if he found the marriage unsatisfactory. There was precedent for polygamy and concubinage as a fallback option. He could follow the venerable example of the patriarchs, judges, and Hebrew kings. That was never explicitly forbidden in divine law. He didn't have to replace his wife, but add another sexual partner to the household. Technically, he was still married to his first wife, but in practice she was passed over in the new arrangement. Put in abeyance. We don't know how many Jewish men took advantage of that tradition, but at least in principle, it was their ace in the hole. 

Yet when Jesus goes back to the creation account to overrule the Mosaic law code, he's presenting monogamy as the archetypal ideal. That blockades polygamy and concubine as escape routes. That's a new move, by forbidding what the Mosaic law permits. He delegitimates that option.