27 After all these things, in the conclusion of the prayer comes a brief clause, which shortly and comprehensively sums up all our petitions and our prayers. For we conclude by saying, “But deliver us from evil,” comprehending all adverse things which the enemy attempts against us in this world, from which there may be a faithful and sure protection if God deliver us, if He afford His help to us who pray for and implore it. And when we say, Deliver us from evil, there remains nothing further which ought to be asked. When we have once asked for God's protection against evil, and have obtained it, then against everything which the devil and the world work against us we stand secure and safe. For what fear is there in this life, to the man whose guardian in this life is God?
Source: The Treatises of Cyprian (New Advent)