In many religions, the supreme deity (God) is given the title and attributions of Father. In many forms of polytheism, the highest god has been conceived as a "father of gods and of men". In the Israelite religion and modern Judaism, God is called Father because he is the creator, law-giver, and protector. In Christianity, God is called Father for the same reasons, but especially because of the mystery of the Father-Son relationship revealed by Jesus Christ. In general, the name of Father applied to deity signifies that he is the origin of what is subject to him, a supreme and powerful authority, a patriarch, and protector.
Islam, however, does not see Allah in a fatherhood role. For Muslims, such a relationship with him is condemned by the Qur'an. "(Both) the Jews and the Christians say, 'We are sons of Allah and His beloved'. Say: why then doth He punish you for your sins? Nay, you are but men of the men He has created". (Surah 5:18)
To Christians, God the Father's relationship with humanity is as a father to children. Thus, humans in general are sometimes called children of God. To Christians, God the Father's relationship with humanity is that of creator and created beings, and in that respect he is the father of all. The New Testament says, in this sense, that the very idea of family, wherever it appears, derives its name from God the Father (Ephesians 3:15), and thus God himself is the model of the family.
However, there is a deeper sense in which Christians believe that they are made participants in the eternal relationship of Father and Son, through Jesus Christ. Christians call themselves adopted children of God: But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, to redeem those who were under the law, that we might receive the adoption as sons. And because you are sons, God has sent forth the Spirit of His Son into your hearts crying out, "Abba, Father!" Therefore you are no longer a slave but a son, and if a son, then an heir of God through Christ. (Epistle to the Galatians 4:4-7)
The expressions "God the Father" and "God our Father" appear frequently in the New Testament, as does Son of God, while God the Son and "God the Holy Spirit" are absent. Patristic and liturgical texts include the phrase "the God and Father, which is also used by Cyril of Alexandria. Basil the Great in one passage speaks of "God the Father and God the Son" (ep. 52:1), but he writes elsewhere: "There is one God and Father, one only-begotten Son, and one Holy Spirit. Thus, while the classic Christian teaching is that the Father is God, the Son is God, and the Holy Spirit is God, this does not appear to be matched by equal usage of the phrases "God the Father", "God the Son", and "God the Holy Spirit" in early Christian writing. Likewise, the popularity of such expressions as "God the Father, God the Son, and God the Holy Spirit" (which might be criticized as having a modalistic flavor) appears to be of more recent origin. While such language departs from New Testament usage, the undoubted deity of the Son and the Spirit according to classical Christianity legitimates its use. Still, it is notable that the biblical expression "God the Father" -- and absence of similar expressions relative to the Son and Spirit -- lays stress on the unique monarchy of the Father.
Other Christians held alternative ideas about the Trinity. A handful have described the Father, Son and Spirit as each a distinct, eternally existent being (tritheism), or as a different "manifestation" of a single being (modalism). Some have theorized that the relationship of Father and Son began at some point probably outside of normal "history" (Arianism); and others have believed that God became a Father when he uttered his creating Λογος ("logos" or "word"), who is both a principle of order and a living being to whom God bears the relationship as Father (some gnostics). Others found strong affinity with traditional pagan ideas of a savior or hero who is begotten by deity, an idea of the Father similar to Mithraism or the cult of the Roman emperor.
For many Christians, the person of God the Father is the ultimate, and on occasion the exclusive addressee of prayer, often in the name of Jesus Christ. The Lord's Prayer, for example, begins, "Our Father who art in Heaven…"
In the New Testament, God the Father has a special role in his relationship with the person of the Son, where Jesus is his Son and his heir (Epistle to the Hebrews 1:2-5). According to the Nicene Creed, the Son (Jesus Christ) is "eternally begotten of the Father", indicating that their divine Father-Son relationship is not tied to an event within time or human history. See Christology.
In Eastern Orthodox theology, God the Father is the "arche" or "principium" (beginning), the "source" or "origin" of both the Son and the Holy Spirit (which gives intuitive emphasis to the threeness of persons); by comparison, Western theology explains the "origin" of all three hypostases or persons as being in the divine nature (which gives intuitive emphasis to the oneness of God's being). The Cappadocian Fathers used this Eastern Orthodox monarchian understanding to explain why trinitarianism is not tritheism: "God is one because the Father is one," said Basil the Great in the fourth century. In the eighth century, John of Damascus wrote at greater length about the Father's monarchial relation: