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

Heidelberg Catechism

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

Answer. 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.[1]

[1] Isa 63:16; Mt 7:9-11; Lk 11:11-13; 1 Pt 1:17