Jesus said the two become one

The objection

Jesus said the two become one flesh, therefore a man can only have one wife. He didn't say the 'three' become 'one' flesh, or the 'four' become 'one' flesh.

The answer

Jesus was responding to a question from the Pharisees about divorce, not addressing the issue of polygyny directly. The Pharisees asked:

Is it lawful for a man to divorce his wife for any and every reason? - Matthew 19:3

Jesus quoted Genesis 2:24 in his reply:

For this reason a man shall leave his father and his mother, and be joined to his wife; and they shall become one flesh. - Genesis 2:24

He then added:

So they are no longer two, but one flesh. What therefore God has joined together, let no man separate. - Matthew 19:6

Key Points to Consider

Jesus' focus was on the permanence of the marriage bond, not on how many marriages a man has or can have.

The use of "two become one" in the context of divorce was to emphasize the permanence of the marriage bond, not to address polygyny.

Jesus was illustrating that when God joins two people together, no man should separate that union.

A man taking another wife to himself is not severing the one flesh union of the first wife, but rather he is adding another woman to his body, in a separate one flesh union. Just as we are all added individually to the body of Christ in "one spirit" as Paul describes in 1 Corinthians 6:

Or do you not know that the one who joins himself to a prostitute is one body with her? For He says, 'THE TWO SHALL BECOME ONE FLESH.' But the one who joins himself to the Lord is one spirit with Him. - 1 Corinthians 6:16-17

Implications for Divorce

Jesus' teaching implies that unlawfully putting away a wife (without biblical justification) goes against God's design for marriage.

The unity described ("one flesh") suggests that breaking apart a marriage is akin to dividing a single entity.

The phrase "what God has joined together" emphasizes the divine nature of the marriage bond.

Conclusion

This passage, when understood in its context, is primarily a teaching about the sanctity and permanence of marriage, aimed at discouraging divorce. While it uses language that refers to two individuals, its main thrust is not to define the number of people in a marriage but to emphasize the binding nature of the marital commitment in God's eyes.

Remember, the question they were asking was about divorce, and they were trying to trap him into saying that it was lawful for a man to divorce his wife for any reason. Jesus was simply answering their question by quoting Genesis 2:24 and emphasizing the permanence of the marriage bond.