Obviously that small verse at the end of the text for this weekend gives people a lot of trouble. And I can see why. At Matthew 5:48, Jesus says, "You therefore must be perfect, as your heavenly Father is perfect."
First of all, I'm not sure that it's helpful to have the word 'must' there. It's not in the original text. The text simply says, "You, therefore, be perfect...." The word 'must' certainly adds something to the text. When you add a word like 'must', then you can start to treat it like a 'should', and that's a completely different thought. (I, for one, think that the current translation of the Small Catechism, with the meanings of the Commandments, is a really bad one. Instead of 'We should fear and love God...," I would prefer, "We are to fear and love God....")
If you think that by these translations I'm making it even more difficult for us to do them, then you are exactly correct. The sooner we give up on trying to do these things, the better.
We definitely need some help to be perfect. And we can't get away from the meaning of the word 'perfect'. Although the Greek word can refer to attaining an end or purpose, it describes God. He didn't evolve toward an higher end or purpose after billions of years. He is and has always been perfect.
I should have said in the previous paragraph that this describes our heavenly FATHER. That's certainly a clue that God is willing and even eager to give out some gifts.
The Beatitudes near the end with saying that the pure in heart will see God and that the peacemakers will be called sons of God. I think that's also a significant clue to say where Jesus is headed with this insurmountable task. We need a lot of help, and, in church, we've come to the right place.
That could well be the theme of this entire account, even with all its sermons: Jesus is our Savior, our Rescuer. Near the middle of this sermon he's going to say to the disciples that they shouldn't be like the hypocrites who show off. At the end of this sermon he's going to call God 'HIS Father (not YOUR Father any more)', and he's also going to tell the disciples to listen to his words and do them.
And so we continue to follow him. It's not too difficult to see where he's headed with this.