There is a war between Good and Evil. Good will win, but Evil must be taken seriously. In fact, for most of human history, it must appear as though Evil is the stronger of the two powers. But the Gospel proclaims Evil has an expiration date.
The crucifixion of Jesus Christ exhausted the power of Evil. Every imaginable Evil was poured onto Jesus, and it killed him. Evil unleashed the full measure of its power, and there was nothing left for Evil to do once Christ had died. Evil was finished.
Later, when Christ resurrected, Evil remained exhausted. There was still nothing Evil could do, since its final weapon was death and death could no longer contain the Risen Lord.
Adapted from Dying for a Fix