The Mother of Prophetic Narratives

The angel Gabriel appears to the prophet upon whom he would be peace and instructs him about Islam. There's an extraordinary just a couple of sentences where Gabriel says to the prophet, talking about the future, the slave girl shall give birth to her mistress. And you will see barefooted naked destitute beduins competing in the construction of towering buildings. I mean, why is this a death so important? And in what ways does this come true?