“Our father is Abraham” - that was the protest of the Jews to Christ yesterday, and today fills in the background to that claim. We're brought back to Abraham and the first covenant, to God swearing His half and laying out the covenant promises. The covenant is not between them only, but extends to all of Abraham's descendants; they have only to keep the covenant and everything that God promised will be theirs.
They've kept the covenant, by fits and starts, but they do not understand what all of it was pointing to. Abraham did – Jesus tells them that he “rejoiced to see my day; he saw it and was glad.” But they are not; they are not true children of Abraham, and they do not take kindly to Christ saying so. Their belief in Him begins to shred; they question Jesus again, in more hostile words, and when He again lays claim to divinity they try to stone Him.
They aren't so different from the Jews of Jeremiah's day, who heard only what they wanted to hear. They aren't so different from anyone living today. Who really wants to know the full truth of himself? If we've been staying the course in Lent, we've been stripped of some comforts. We've lost some illusions. We're a little more ready to know those truths, and the Truth will soon be lifted up for us.