Why was Mut'ah (temporary marriage) made lawful then unlawful, then lawful then unlawful, and why would the Messenger, may Allah's prayers and peace be upon him, make lawful something he had previously forbidden, or something abhorrent, even if for a temporary period?

Scholars have differed regarding the repeated abrogation of the ruling on temporary marriage (mut'ah). While al-Nawawi favors repeated abrogation, Ibn al-Qayyim holds that it was not repeated, and that the prohibition occurred during the year of the Conquest (of Mecca). The correct view is that temporary marriage was prohibited during the year of the Conquest, due to the established fact that the Companions engaged in it with the permission of the Prophet, peace and blessings be upon him, in that year. If it is asked: why was it permitted and then prohibited? The answer is that this is from Allah Almighty, not from the Messenger Himself, peace and blessings be upon him. Two points should be noted: First, seeking wisdom in Allah's rulings is for reassurance and confirmation; otherwise, Allah Almighty does what He wills and is not questioned about His actions. Second, there is no contradiction between the prohibited temporary marriage being considered zina (fornication/adultery) and its being permissible previously. It was not zina at the time of its permissibility, but the term zina was applied to it metaphorically after its prohibition to emphasize its sacredness.