If you want to know why we call our God Father, listen to Moses: Is not He thy Father that hath bought thee? Hath He not made thee, and established thee? (Deut. 32:6).

Listen, too, to Isaiah: O Lord, Thou art our Father; we are the clay, and Thou our potter; and we all are the work of Thy hand (Is 64:8). Under prophetic inspiration, Isaiah speaks plainly. God is our Father, not by nature, but by grace and by adoption.

Paul too was a father: father of the Christians in Corinth. Not because he had begotten them according to the flesh, but because he had regenerated them according to the Spirit.

Joseph too was called father of Christ, not as procreator in a physical sense, but as His guardian: he was to nourish and protect Him.

With greater reason God calls Himself Father of human belongs and wants to be called Father by us. What unspeakable generosity! He dwells in the heavens; we live on the earth. He has created the ages; we live in time. He holds the world in His hands; we are but grasshoppers on the face of the earth. — St. Cyril of Jerusalem, Catecheses