How did the Son of God become human?
He came down from heaven, was incarnate of the Holy Spirit and the Virgin Mary and became truly human.
Catechism for the Global Methodist Church, question 11
18The origin of Jesus Christ was thus: his mother Mary having been betrothed to Joseph, before they came together she was found with child from the Holy Spirit.
30And the angel said to her, "Do not fear, Mary, for you have found favor with God." 31And behold, you will conceive in the womb and bear a son, and you will call his name Jesus. 32He will be great and will be called Son of the Highest, and the Lord God will give him the throne of his father David. 33He will reign over the house of Jacob forever, and his kingdom will have no end. 34Mary said to the angel, "How will this be, since I do not know a man?" 35And answering, the angel said to her, "The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore the one being born will be called holy, Son of God."
1In the beginning was the Word, and the Word was with God, and the Word was God. 2This one was in the beginning with God. 14And the Word became flesh and dwelt among us; we have seen his glory, the glory as of the unique one from the father, full of grace and truth.
3concerning his son, who came from the seed of David according to the flesh, 4who was declared the son of God with power according to the spirit of holiness by the resurrection from the dead: Jesus Christ our Lord
4But when the fullness of time had come, God sent forth his Son, born of a woman, born under the law.
6Who, existing in the form of God, did not consider equality with God a thing to be grasped. 7But he emptied himself, taking the form of a slave, being born in the likeness of humans, and being found as a human. 8He humbled himself, becoming obedient until death, even death on a cross.
1:1That which was from the beginning, that which we have heard, that which we have seen with our eyes, that which we looked at, and our hands touched concerning the word of life. 1:2The life was revealed, and we have seen it and testify and proclaim to you the eternal life that was with the Father and was revealed to us. 1:3What we have seen and heard we also proclaim to you, so that you too may have fellowship with us; and our fellowship is with the Father and with his Son, Jesus Christ. 4:2By this you know the Spirit of God: every spirit that confesses Jesus Christ has come in the flesh is from God.
This question moves the catechism from who the Son is to what the Son did. The answer is the second half of the creed's incarnation clause, and the church's doctrinal standards say the same thing in their own words. Article II of the Articles of Religion teaches that the Son, "the very and eternal God," "took man's nature in the womb of the blessed Virgin." Article II of the Confession of Faith calls him "the eternal Word made flesh, the only begotten Son of the Father, born of the Virgin Mary by the power of the Holy Spirit."
He came down from heaven means the one who was born in Bethlehem existed before Bethlehem. John says of the Word that he "was in the beginning with God" (John 1:2), and Paul describes him as "existing in the form of God" before he "emptied himself, taking the form of a slave, being born in the likeness of humans" (Philippians 2:6-7). Incarnate of the Holy Spirit and the Virgin Mary names how it happened. Matthew records that Mary "was found with child from the Holy Spirit" (Matthew 1:18), and the angel answers Mary's own question with the words, "The Holy Spirit will come upon you, and the power of the Highest will overshadow you" (Luke 1:35). There was no human father, and Mary was the true mother, so that the child came "from the seed of David according to the flesh" (Romans 1:3) and was "born of a woman, born under the law" (Galatians 4:4).
Became truly human guards against the oldest error about Jesus, which was that he only seemed to have a body. John insists on what the apostles saw with their eyes and their "hands touched concerning the word of life" (1 John 1:1), and he makes the confession that "Jesus Christ has come in the flesh" the test of a true spirit (1 John 4:2). Article II of the Articles of Religion says the Godhead and Manhood "were joined together in one person, never to be divided."
For a Methodist this teaching is the ground of confidence that God knows human life from the inside. Every prayer offered in Jesus' name rests on the fact that the Word "became flesh and dwelt among us" (John 1:14) and shared the body and the death of the people who pray. Wesley preached the incarnation as the beginning of the work of salvation, the Son taking human nature so that human nature could be healed.