Grace
The promises that God made to Israel in the Hebrew scriptures were impossible ones to keep. God promised them land and status and a great future, and the people gladly seized the promise. Yet the conditional nature of the promise became clear as Israel lost bit by bit the treasures of their election. So Israel was traumatized by a god who they thought had failed them. On the other hand, the prophets told of the trauma of god who had been betrayed by the people. Yet Israel was in an impossible situation. No people will ever keep any law, because the very nature of being a people means to draw boundaries that both include and exclude. This belonging is always more important than obedience. The people will gladly violate the law if it makes them feel more comfortable with who they are as a people.
There is only one promise God can truly keep, and that is a promise that depends on God's will alone. The response of the people cannot effect God's promise in any way. The only promise God can keep is one that says, “I will save you no matter what you do. In fact, you are already saved whether you know it or not. I promise that I will not change that reality nor will I punish you in the short or the long term for how you respond to it. I will love you no matter what. You cannot make me stop loving you.” God's promise is universal salvation without exception or condition.
We have always assumed that God could make this promise if God wished. Much of our anger against God comes because of God's refusal to make that promise even though it is the only promise that could make any difference. Yet God did make the promise when Jesus died on the cross. For over 2000 years, theologians have been trying to argue against the promise, claiming that the new covenant was just a spiritualized version of the old quid pro quo. But God did make the promise, and even those who refuse to believe it will yet be the recipients of God's joyous, cleansing, life changing grace.