Mormons believe it was the same with polygamy. He normally does not require it. but he specifically required it for a time. Then he discontinued it.
I have heard various reasons why put forward in discussions with other Mormons about why polygamy was practiced and why it was then discontinued. Some of the explanations sounded better than others. But they were all just that, explanations. I don't claim to know why God commanded it. I have some interesting ideas. But for me it is a matter of faith. I have Faith in God that he commanded it at that time. Most Mormons that try to explain exactly why are usually just giving conjecture.
So how do you explain what Brigham Young taught, that polygamy MUST always be practiced, and then some other leader of the church says no, we gotta stop that.
That is my problem with the Mormon church, policy can change like the wind. That would really suck. Never knowing if whats O.K. today is still gonna be o.k. tomorrow.