en_tn_lite_do_not_use/mat/19/05.md

He who made them also said, 'For this reason ... flesh.'

Alternate translation: "And surely you know that God also said that for this reason ... flesh."

For this reason

This is a part of the quotation from Genesis story about Adam and Eve. In that context the reason a man will leave his father and mother is because God created a woman to be the man's companion.

join to his wife

"stay close to his wife" or "live with his wife"

the two will become one flesh

Alternate translation: "they will become like one person"