Only Son of God
From the Catechism of the Catholic Church, Simplified
"Son of God" - A Human Title (441)
In the Old Testament, the title "son of God" (denoting an intimacy with God) was given to angels, the children of Israel and to kings. Therefore, those who called Jesus "son of God" were not implying that Jesus was more than human.
A Divine Sonship (442-443)
Peter said, "You are the Christ, the Son of the living God" (Mt 16:16). Jesus said that this was revealed by his heavenly Father. (Mt 16:16-17). Paul said that God "was pleased to reveal his Son to me" (Gal 1:15-16) and Paul proclaimed in the synagogues that Jesus "is the Son of God." In these instances, Peter and Paul were speaking of Christ's divine sonship, the very center of apostolic faith.
Earlier, when Jesus was asked by the Sanhedrin "Are you the Son of God?" he answered "You say that I am" (Lk 22:70). Also, Jesus said he was "the Son" who knew the Father in a unique way (Mt 11:27). Jesus clearly distinguished his sonship from others. He always said "my Father" and only in prayer taught the disciples to say "Our Father." After his Resurrection he emphasized this when he said to Mary Magdalene "my Father and your Father" (Jn 20:17).
The Father's Voice (444-445)
At Jesus' Baptism and Transfiguration the Father designated Jesus as his "beloved Son" (Mt 3:17, 17:5). When Jesus called himself the "only Son of God" (Jn 3:16) he affirmed his eternal preexistence. The Centurion's words "Truly this man was the Son of God" is a Christian profession of faith. Only after the Resurrection can the believer give "Son of God" its full meaning.
By his Resurrection Jesus was "designated Son of God in power" (Rom 1:3). The apostles confessed "We have beheld his glory, as of the only Son from the Father" (Jn 1:14).
The Name "Lord" (446)
In the Old Testament, Kyrios (the Greek word meaning "Lord'") indicated the divinity of Israel's God. This word Kyrios ("Lord") is used in the New Testament for the Father and for Jesus, thereby recognizing Jesus as God.
During His Lifetime (447)
David wrote, "The Lord said to my Lord" (Mt 22:41-46). Jesus used this sentence to proclaim his divinity to the apostles. Jesus showed his divine sovereignty by his power over illness, death and Satan. When people gave Jesus the title "Lord" they recognized a divine mystery of Jesus.
The Post-Resurrection Meaning (448-451)
Thomas said, "My Lord and my God" (Jn 20:28), a title of adoration. The disciples said, "It is the Lord" (Jn 20:28, 21:7), a title of affection. By calling Jesus "Lord," the New Testament affirms that the honor due to the Father is also due to Jesus because he "was in the form of God" (Phil 2:6).
Believing in Christ's unique lordship, Christians refused to submit totally to any earthly power. Caesar was not "the Lord" because "the kingdom of the world now belongs to our Lord and to his anointed" (Rev 11:15). The purpose of all human history is Jesus, the world's Lord and Master.
Christian prayer is filled with the title "Lord." Scripture concludes in hope: "Amen. Come, Lord Jesus!" (Rev 22:20).
Why Did Jesus Come? (456-459)
Jesus was made man "for our salvation." The Word became flesh to reconcile us with the Father (4:14). "As captives, we awaited a Savior; as prisoners, help; as slaves, a liberator. Did not these things move God to descend to human nature?" (St. Gregory of Nyssa). God sent his Son "so we might live through him" (1 Jn 4:9), and so we "should not perish but have eternal life" (Jn 3:16).
Jesus is our model. He said "Learn from me" (Mt 11:29). The Father commanded us to "Listen to him" (Mk 9:7). Jesus told us to "Love one another as I have loved you" (Jn 15:12).
Our Gift (460)
By becoming flesh, Jesus made us "partakers of the divine nature" (2 Pet 1:4). "The Word became man so that man might become a Son of God" (St. Irenaeus). "For the Son of God became man so that we might become God" (St. Athanasius). Jesus "assumed our nature, so that he, made man, might make men gods" (St. Thomas Aquinas).
Becoming Flesh - The Incarnation (461-462)
The Church calls Jesus' assuming a human nature the Incarnation. Jesus "took the form of a servant, being born in the likeness of men" (Phil 2:7). "A body have you prepared for me... then I said, Lo, I have come to do your will, O God'" (Heb 10:5-7).
The Unique Christian Belief (463)
The distinctive sign of the Christian faith is belief in the Incarnation. God's Spirit reveals to the believer "that Jesus Christ has come in the flesh" (1 Jn 4:2). God "was manifested in the flesh" (1 Tim 3:16).