The way I see it:
God promised to give Adam, Eve, and their descendants over to death. Why? Because they broke the covenant: all transgressors must die. In a sense, God almost had an “agreement” with death. The guilty die.
But Death got greedy. He overstepped the terms of the agreement. He tried to take the only person in the history of the whole world who had not actually broken the covenant: he tried to take the one person to whom he had no right. Christ. And Death was swallowed up by the victory that he tried to conquer. The covenant with Death was broken, and God began to work things backwards. Now Death has no hold on any of us, because Death tried to hold onto Christ. And because we hold to Christ, Death has no power over us.
The grave is empty.