Galatians 4:6 "Because you are His sons, God send the Spirit of His Son into our hearts, the Spirit who calls out, "Abba, Father!"

Abba is directly translated to mean father, where in this case it would be personal to mean "my father". This instills the direct relationship that we have with God and God with us. We are His children and in turn He is our father, and through the Holy Spirit and the dying, resurrection and ascension of Jesus Christ we are heirs and have every right to call Him father.