God doesn't tempt us to sin (James 1:13), but he does bring us into trials in which we may fall to sin. To pray, "lead us not into temptation" is asking God to give us the grace we need to glorify him and our Savior by fleeing and resisting sin. "Deliver us from the evil one" is praying from the complete defeat of Satan. Just as the fifth petition dealt with the issue of our guilt ("forgive us our debts"), this petition speaks to our need for the Spirit's power to overcome sin from every source.