But why do you pray God not to lead you into evil, when this is the proper office of Satan the devil?

As God by His mercy preserves the faithful, and does not permit the devil to seduce them, or sin to overcome them, so those whom He means to punish He not only abandons, and deprives of His grace, but also yields to the devil to be subjected to his tyranny, blinds them and delivers them over to a reprobate mind.