The followers of Jesus Christ do not call Jesus the Son of God out of enthusiasm and emotion, or from force of habit. Rather, this title comes from the Word of God. Christians call Jesus the Son of God because, according to the Gospel of Luke, chapter 1, verse 35, Mary became pregnant by the Holy Spirit, that is, the Holy Spirit of God. This is why her baby, Jesus, is called the Son of God. Even 700 years before the birth of Jesus, it was prophesied in the Old Testament that a pregnant virgin would give birth to a son and he would be called “Immanuel”, which means "God is with us".