8 But if any one wishes to learn how we call God “Father,” let him hear Moses, the excellent schoolmaster, saying, Did not this your Father Himself buy you, and make you, and create you? Also Esaias the Prophet, And now, O Lord. You are our Father: and we all are clay, the works of Your hands. For most clearly has the prophetic gift declared that not according to nature, but according to God's grace, and by adoption, we call Him Father.
Source: Catechetical Lectures (New Advent)