Slaves under an oppressive regime, literally worked to death. And when God comes and introduces himself to them by name, their cultural memory of him and his last communication with them being four hundred and thirty years prior, he tells them something amazing.
Their biggest problem isn't the one they can see. Yes, they are slaves. Yes, the government is evil and wicked. Yes, Yahweh is going to rescue them from their geopolitical and economic reality but what He has really come to do is rescue them from their sins. From a curse which if they knew it at all was merely a part of their creation myth. He has come to rescue them from eternal death. And he even hints at how He's going to do it.
Somewhere around two thousand years later a man comes to the same people, now subjects under a foreign empire in their own land. This man sits down to another Passover dinner, now not much more than a religious ceremony that establishes their cultural and racial heritage, and tells them something amazing. Their biggest problem isn't occupation forces and pagan governors, it is still not geopolitical and socio-economic.
He tells them He is God, and he's what Passover was all about.