Genesis chapter one reveals the peculiar three-person nature of the Christian god: "Then God said, 'Let us make mankind in our image...'" (New International Version, Gen. 1.26). God refers to himself with this singular-yet-plural description throughout the Old and New Testaments: "The man has now become like one of us..." (Gen 1.26) and "...make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit..."(Matt. 28.19). Unlike the Hindu god Shakti, who has numerous manifestations, or the Triple Goddess of Neopaganism, a single female being in three different stages of life, the expresses himself as a single entity comprised of three different persons. Besides providing a fascinating topic for theologians, why is the Trinity one of the basics of Christianity?
The strict monotheism of Christianity is underscored by the three-person kinship of god. If the Christian god is not a mere individual, but three equal and inseparable persons who exist in mutual love and agreement, then god's most essential characteristic is relationship; god shares and receives and cannot be defined outside of mutual intimacy. This explains why the god of the Bible forbids the worship of any other god beside him; like a consumed lover, he wants the object of his affection to have eyes for him alone: "Do not worship any other god, for the Lord, whose name is Jealous, is a jealous God" (Exod. 34.14). God calls the worship of other deities "prostitution" (Ezek. 23.7) and addresses his beloved people, Israel, as a wife of whom he expects fidelity: "...you will call me 'my husband;' you will no longer call me 'my master.’ I will remove the names of the Baals from her lips..." (Hos. 2.16-17). The Christian god exists as an ultimate, animate union, and so he requires undivided relationship from his followers.
God's three-person essence gives the individual Christian a framework through which she can personally understand him. In the Lord's prayer god is addressed as "Our Father in heaven" (Matt. 6.9), which characterizes god not only as a parental provider and protector, but also as an otherworldly being who is not confined to the physical world humans can see and touch. Through the person of Jesus, who is both human and divine, a Christian can experience god as brother and friend: "For we do not have a high priest who is unable to empathize with our weaknesses, but we have one who has been tempted in every way, just as we are..." (Heb. 4.15).
The Holy Spirit and final person of the Trinity enables the Christian to feel and live out god's constant presence and power: "But you know [the Spirit], for he dwells with you and will be in you" (John 14.17). The accord between the individual Christian and god becomes more intimate with each person of the Trinity; to the Christian, god is at once a divine father who cannot be contained by matter, a vulnerable brother who struggled through all of life’s triumphs and failures, and a kindred soul-mate who acts as a perpetual internal guide and confidant.
The structure of the Christian church is patterned after god's three-person nature. Just as god is one entity made up of separate but equal persons, the church is made up of individuals who do not lose their distinct identities but cannot truly function outside of contact with others. This is why St. Paul compares the Christian church to a human body in Corinthians: "Now if the foot should say, 'Because I am not a hand, I do not belong to the body,' it would not for that reason stop being part of the body...As it is, there are many parts, but one body" (1 Cor. 12.15, 20). Through god, the supernatural connection between Christians cannot be broken by mere words or attitudes because the individual Christian exists as part of a whole.
While the Christian has a unique individual connection with god, this bond is fully realized when it is shared with others: "For where two or three gather in my name, there am I with them" (Matt. 18.20). Additionally, Christians are told to address each other as "brother" and "sister" due to the fact that they are children of the same Father god and siblings of Jesus, the son of god: "For whoever does the will of my Father in heaven is my brother and sister and mother” (Matt. 12.50). Like the single-yet-plural character of god, the church is one entity comprised of familial ties between many individuals.
From the beginning of the Bible to the end, god's three-person nature is one of the basics of Christianity because it emphasizes and shapes the relationship between god and himself, god and the individual Christian, and god and the church.