The Trinity is the doctrine that in the unity of the One God, there are three divine persons: the Father, Son, and Spirit, distinct from one another yet of one substance. The three persons are co-eternal and uncreated: "the Father is God, the Son is God, and the Holy Spirit is God, and yet there are not three Gods but one God." Jesus is understood by Trinitarian Christians to be the person of the Son, eternally begotten by the Father, who came upon earth to deliver to the world.
Such language appears in Matthew 28:19, "Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit." This was incorporated into baptismal formulae, which also invoked a renunciation of Satan, contrasting the initiate's belief in the One God with the idolatry of polytheistic paganism. This language also appears in early doxologies (Galatians 5:25; Romans 8:9; Hebrews 13:15). The doctrine found full articulation with the Council of Nicaea.
The only Son of God
According to the predominant Christian interpretation, the title "Son of God" is understood as an expression of Jesus' divinity, specifically his unique divine sonship as the Second Person of the Trinity.
The title is applied often in the Gospels, notably at the Baptism and the Transfiguration (Matthew 3:17, Matthew 17:5). Also significant is the confession of Peter: "You are the Christ, the Son of the Living God" (Matthew 16:16). Jesus applies the title "the only Son of God" to himself in John 3:16 and John 10:36. John's gospel uses the title as a short formula for expressing his divinity: "We have beheld his glory, glory as of the only Son from the Father, full of grace and truth" (John 1:14).