This pronouncement is based on Deuteronomy 24:1–4. There is no command to issue a certificate of divorce when there is a divorce. This is based on an existing practice. And that is seen by those who explain this as a command for when a divorce happens. The Jews were proud of it, that a divorce with them was officially taken care of as compared to the heathen nations, where there was no set regulation for a divorce.
31 “It was also said, ‘Whoever divorces his wife, let him give her a certificate of divorce.’