Patēr appears 413 times in the NT (making it one of the most common nouns) and carries the full range of paternal meaning. Biologically, it refers to immediate fathers and male ancestors ('Father Abraham'). Socially, it is an honorific for teachers and respected elders. Most profoundly, it is Jesus's primary designation for God — and the designation with which he taught his disciples to address God in prayer: 'Our Father' (Pater hēmōn, Matthew 6:9). The intimacy of Abba (Aramaic for 'father,' used by Jesus in Gethsemane: Mark 14:36) shocked first-century Jews with its unprecedented closeness.
Jesus's use of Patēr for God was revolutionary. While the OT occasionally speaks of God as father (Psalm 103:13; Isaiah 64:8), it was rare and largely national/corporate. Jesus addressed God as Patēr consistently, personally, and intimately — and invited his disciples into this same relationship. Paul declares that believers receive 'the Spirit of adoption by whom we cry out, Abba, Father' (Romans 8:15; Galatians 4:6) — the same cry Jesus used. The entire structure of Christian prayer, identity, and ethics flows from calling God 'Father.' The Johannine literature especially develops the Father-Son relationship as the inner life of the Trinity into which believers are invited (John 14-17; 1 John 3:1).