Where does it say in the Bible there will be seven women for one man?
There is a prophecy in Isaiah 3:16-4:1, which concludes, “And in that day seven women shall take hold of one man, saying, We will eat our own bread, and wear our own apparel; only let us be called by they name, to take away our reproach.”
I think this needs some explanation. The entire section of Isaiah’s prophecy is saying that the northern ten tribes of Israel will be destroyed because (in part) of the harlotry of the women. Then in 4:1 he is saying that after the Assyrians destroy Israel there will be so many women left without husbands that they will beg men to marry them just so their shame at being husbandless will be taken away. Note that they even say they will live their own lives, just so long as they can be called someone’s wife.
Isaiah is certainly not prophesying that in general, and in good times, every man will have seven women. It is a very negative prophecy. It is even negative for the men, because what he is really saying is that approximately seven out of every eight men will be killed.