My understanding has always been, to oversimplify it somewhat, that Yahwism evolved into what scholars call Second Temple Judaism over the period of the Kingdoms and the Babylonian Exile, with the major change being the shift from polytheism to monotheism. Only two of the original twelve tribes remained in Jesus’ time, ten were dispersed and assimilated after the Assyrian destruction of the northern kingdom and vanished from history as identifiable groups. But I’ve never perceived Jesus’ purpose as being to reunite the remaining two, he’s portrayed as bringing a new covenant for everyone.Yahwism and Judaism weren't compatible.
So which tribes were Jesus sent to reunite?
Which I also think is BS, he was just one of many messianic apocalyptic preachers the political turmoil of his times drew forth, and for reasons I don’t fully comprehend, only his message survived into our day. Paul’s travels and writings were certainly major factors though, nobody else had a bulldog like him spreading the news. Judaism rejected him because it was anticipating a political and military leader who would re-establish the glory days of the old kingdom, not some soft-headed spiritualist who’d take no role in the mundane affairs of this world.