What is the ruling on one who divorced his wife in jest many times, being ignorant of the ruling, and whose intention was not divorce?

Explicit divorce pronouncements effectuate divorce, even if the husband is jesting, as long as he intended to utter them. This is based on the Prophet's (peace be upon him) saying: "There are three matters, serious when serious and serious when in jest: marriage, divorce, and رجعة (revocation of divorce)." There is no difference between one who knows the ruling and one who is ignorant of it, unless he was coerced.