Since God allows Satan to exist, why should we pray for him to be crushed?

I am reading *An exorcist tells his story*, and in it the author discusses a prayer by Pope Leo XIII: > St. Michael the Archangel, defend us in battle. Be our defense against the wickedness and snares of the Devil. May God rebuke him, we humbly pray, and do thou, O Prince of the heavenly hosts, by the power of God, thrust into hell Satan, and all the evil spirits, who prowl about the world seeking the ruin of souls. Amen. So the pope here is praying for God to thrust Satan into hell, but why? Wouldn't this demand go against God's will, who in fact allows Satan to roam and have certain influence?