God willed that many things should be said by the prophets, his servants, and listened to by his people. How much greater are the things spoken by the Son. These are now witnessed to by the very Word of God who spoke through the prophets. The Word of God does not now command us to prepare the way for his coming: he comes in person and opens up the way for us and directs us toward it. Before, we wandered in the darkness of death, aimlessly and blindly. Now we are enlightened by the light of grace, and are to keep to the highway of life, with the Lord to precede and direct us.
The Lord has given us many counsels and commandments to help us toward salvation. He has even given us a pattern of prayer, instructing us on how we are to pray. He has given us life, and with his accustomed generosity, he has also taught us how to pray. He has made it easy for us to be heard as we pray to the Father in the words taught us by the Son.
So, my brothers, let us pray as God our master has taught us. To ask the Father in words his Son has given us, to let him hear the prayer of Christ ringing in his ears, is to make our prayer one of friendship, a family prayer. Let the Father recognize the words of his Son. Let the Son who lives in our hearts be also on our lips. We have him as an advocate for sinners before the Father; when we ask forgiveness for our sins, let us use the words given by our advocate. He tells us: Whatever you ask the Father in my name, he will give you. What more effective prayer could we then make in the name of Christ than in the words of his own prayer?
St Cyprian, bishop and martyr, On the Lord’s Prayer (full text here)
Duccio di Buoninsegna, from Maestà (1308-11)