When Pharisees ask Jesus whether a man may divorce his wife "for every cause," they are not introducing the idea of divorce for the first time. They are asking within an existing Jewish discussion about how the Torah's divorce legislation should be interpreted.
Jesus responds by moving behind the dispute over permissible grounds to the creation account itself.
Deuteronomy 24 assumes a written certificate of divorce and describes a case in which a husband sends away his wife after finding something objectionable. Jewish interpreters debated the scope of that wording, with some allowing broader grounds and others taking a narrower view.
A certificate had practical importance because divorce affected a woman's legal and social status and her ability to remarry. Jesus' answer distinguishes Moses' concession in a fallen situation from God's creation intention for marriage.
The background shows that the question is not simply "Is divorce possible?" but "What does the Torah permit, and on what grounds?" Jesus refuses to let the discussion remain only at the level of finding permissible reasons.
By appealing to Genesis, he reframes marriage around God's joining of husband and wife. That move gives the teaching its force within the contemporary debate and explains the disciples' strong reaction to the strictness of his answer.