From the Heidelberg Catechism for the Lord’s Day, November 17

119. What is the Lord’s Prayer?

Our Father who art in heaven, Hallowed be Thy name. Thy kingdom come. Thy will be done on earth, as it is in heaven. Give us this day our daily bread. And forgive us our debts, as we forgive our debtors. And lead us not into temptation, but deliver us from evil: for Thine is the kingdom, and the power, and the glory, forever. Amen.

120. Why did Christ command us to address God thus: “Our Father?”

To awaken in us at the very beginning of our prayer that childlike reverence for and trust in God, which are to be the ground of our prayer, namely, that God has become our Father through Christ, and will much less deny us what we ask of Him in faith than our parents refuse us earthly things.

121. Why is it added: “Who art in heaven?”

That we might have no earthly thought of the heavenly majesty of God, and from His almighty power expect all things necessary for body and soul