In the Our Father we have not merely a plan for addressing God, a formula of prayer, but a command: ‘Thus shalt thou pray'. Prayer is the expression of our attitude towards God. Our Lord says, ‘This is the way you've got to ask God for things—this is the way you've got to think of God and address him; the way I wish you to approach him.'
Take the Lord's Prayer in that sense. ‘What is God to you?’ says our Lord; and he begins ‘Father'.
St Thomas says that we are entitled to take as intended for us every meaning of our Lord's words and actions which they will legitimately bear. Therefore we must take God as an ideal Father. ‘I am your Father, I want you to think of me as your Father; and not merely to think of me but to know that I am your Father.’ Look at a little child and his father; he receives all he has and is from his parents, but quite soon goes on independently of them.