10 And he said, Behold, I make a covenant: before all thy people I will do marvels, such as have not been done in all the earth, nor in any nation: and all the people among which thou art shall see the work of the Lord: for it is a terrible thing that I will do with thee.

Notice how God makes no reference to Israel’s sin or broken promises. He is establishing His covenant as if it is totally fresh, being extended for the first time, with no baggage from previous failures.

Such is the magnanimity of the Lord’s mercy. Because of the atonement of Jesus Christ, transgressions are not merely swept under the rug, they fully die with him, and every new beginning is as pure and perfect as the first. Because Israel sought a way to make restitution, the Lord has already forgiven them, and they are being offered the exact same covenant as before.

The word that the Lord uses towards the end to describe the work that He will accomplish with Israel is translated here as “terrible.” The original word is יָרֵא, which is often used to describe fear, but more broadly can also mean to cause reverence or awe. It suggests something so great that it overpowers the beholder. In the next verses God will specifically mention the driving out of the heathen nations in Canaan, so the application of this word makes sense.