The quote, "If you deem it best for the orphans, you may marry their mothers". Excuse my ignorance but how the hell do you marry an orphan's mother if an orphan isn't supposed to have a mother nor father. Or is there another meaning to it ?
in the times before, women were dependent on their husbands to provide for them/protect them.
when the husbands went to war, they left their children and wives behind. If they died the child becomes an orphan in Islam. You are an orphan if your mother or father or both die.
so since there were alot of wars in early islam times, and alot of men died and left their wives and children behind with non one to take care of them, this have more than wife rule came to be to protect the orphan kids and widow wives.