As the Lord's Prayer comes to a close, we ask to be protected. There is an 'evil one' and we need to be protected from him.
But what does this evil one want to do to us? He's mentioned one other time in the Sermon on the Mount:
"Let your 'Yes" be 'Yes' and your 'No', 'No'; anything beyond this comes from the evil one." (Matthew 5:37, italics mine)
It seems that the evil one likes it when we swear an oath. He likes it when we promise to do something. He likes it when we begin a sentence with, 'to be honest ...'
Maybe you think it's a bit trivial. Shouldn't I be writing about bombings? persecution? the big sins? Yes, that is the risk and it's a big one. But Jesus wants us to be his light for the world, and he wants us to stand against everything that undermines us.
We need to pray because we need God's protection or we fall. Peter would find that out later, when Jesus warned him to watch and pray or he would fall into temptation. The Sermon on the Mount tells us about many ways we can fall: anger, sexual desire, revenge, love of money, doing good things for bad reasons, worrying. We're all prone to these things so we need God's protection or we won't be the bright light that God call's us to be.
So let's pray.