What is the idea that made Christians believe that Jesus, peace be upon him, is the Son of God?

Christians believe that the idea of Christ being the son of God, due to his birth without a father, is invalid, despite the conclusive evidence of his mother's innocence, including Christ's speech in the cradle. They base their belief on him being "the word of God" and "a spirit from Him." The rebuttal to them is easy: God created Adam without a father or mother, and Eve without a mother, so why is it surprising that Jesus was created without a father? The meaning of "the word of God" is that he was created by God's command, and the meaning of "a spirit from Him" is that he is a spirit among the spirits that God created, which He attributed to Himself out of honor, as in His Almighty saying about Adam: "So when I have proportioned him and breathed into him from My [created] spirit, then fall down to him in prostration." And no one has ever said that Adam is the son of God.