We as Christians try to treat everyone with respect. We usually refer to someone by whatever title they have earned through education, such as 'Doctor Smith."  Father, however, has the meaning of "giver of life."  We each have an earthly father, who gave us human life, but a "spiritual father" would be one who has given us life through the Holy Spirit.  The conversion of Cornelius, the Gentile centurion, is an example of that in Acts 11:15-18:  "The Holy Spirit came upon them as he had come on us in the beginning.  Then I remembered what the Lord said, John baptized with water, but you will be baptized with the Holy Spirit….God has granted even the Gentiles repentance unto life."  NIV

God is our only true Father, though none have the right to refer to him as Father unless they have come into a covenant relationship with Him through Christ. Through this relationship, the Apostle John said, "Now are we the sons of God."  I John 3:2  KJV

God is not dealing with the world in general at this time. He is looking for a select few to make up a church of those who are willing to dedicate their lives in sacrifice in order to earn the high calling of heaven. "My one thought is, by forgetting what lies behind me and straining to what lies before me, to press on to the goal for the prize of God's high call in Christ Jesus."  Philippians 3:14  Moffatt

The rest of the world have God's promise to be resurrected from death ("There is to be a resurrection both of the righteous and the unrighteous–the just and the unjust."  Acts 24:15  Amplified) to God's glorious Kingdom here on earth. In the resurrection, God will enter into a new covenant relationship with Israel. “But this shall be the covenant that I will make with the house of Israel:…I will put my Law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.” Jeremiah 31:33. Soon afterward, all mankind will flow to Jerusalem to also enter into that wonderful new covenant. “…all nations shall flow unto it. And many people shall go and say, Come ye, and let us go up to the mountain of the LORD, to the house of the God of Jacob; and he will teach us of his ways, and we will walk in his paths…” Isaiah 2:2,3  Yes, in that glorious day, all mankind will be able to call God, Father! “He that overcomes will inherit all this, and I will be his God and he will be my son.”  Revelation 21:7  NIV