John 12:31

Now is the judgment of this world: now shall the prince of this world be cast out.

The crisis of all ages had arrived. Jesus would die on the cross to redeem men from the curse of sin, enabling them to be saved eternally, and to restore the fellowship with God, broken such a long while before by the disaster in Eden. The head of Satan would now be "bruised" in fulfillment of Genesis 3:15. This great victory is here called the casting out of the prince of this world. That the cosmic victory over Satan would be won by such a thing as the death of Christ on Calvary is the mystery hidden before times eternal. The victory came through death itself, and that at the very moment when Satan might have thought that he had won (Hebrews 2:15). The words Jesus spoke here were in anticipation of that victory.

The prince of this world ... refers to Satan, called also the "god of this world," and "the prince of the powers of the air." The casting out will be accomplished by the cross, as the next verse shows.