Why is Jesus called the Son of God?

Because He is the Son of God.

Because God caused His mother to become pregnant with Him. That's the usual definition of "father".

Because he's God's Son.  Duh.

Jesus lived in heaven as a spirit person before he came  to earth. He was God's first creation , and so he is called the "firstborn"  Son of God . (Colossians 1:15; Revelation 3:14)  Jesus is the only Son that God created by himself.  God Jehovah  used the prehuman Jesus as his "master worker" in creating all other things in heaven and on earth. ( Proverbs 8:22-31; Colossians 1:16,17)

The Bible uses the terms 'Father' and 'Son of God' to show how those two relate to each other. It's the same with the term 'Son of Man' - the Bible uses that to show us how Jesus relates to human beings, for He was fully human. But Jesus wasn't 'just' a sinless (perfect) man who woke up one day and discovered that God was His Father. Adam did. We learn that God spoke with Adam in the breezy part of the day, in the garden of Eden. They were in direct, one-to-one communication. We don't know if that included visual contact. Yet when we learn from the Bible that Jesus was Adam's Maker (John 1:1-14) prior to becoming Mary's child, then the superiority of Christ is light years advanced from the condition of Adam! 

How could He, who was with the Father in the beginning, and who IS God, not know that relatedness when in the flesh, as the man, Jesus? After all, the same Holy Spirit who caused the miracle of the Incarnation was with Christ, right from then through all of His earthly mission. Even by age 12, Jesus astounded religious leaders with His knowledge of the scriptures, for the Holy Spirit was His tutor. He would have read all the prophecies in the scriptures about Messiah, and would know exactly who He was. That was why Jesus continually spoke of His Father in Heaven, even from age 12 - Luke 2:41-52.

The big trap a lot of sincere people fall into, though, is supposing that, just like earthly men who father children, God the Father must have procreated Jesus, so that there was a time when the Son never existed. That is not what the Bible teaches. The Son is the eternal Son, just as the Father is the eternal Father, for they have always related to each other in that special way.

Because his Father is God. 

Here the answer: https://www.jw.org/finder?wtlocale=E&docid=502019180&srcid=share

Jehovah has made it very clear that Jesus is the messiah. God promised to give John the Baptizer a sign so that he would know who the Messiah was. When Jesus went to John to get baptized in the Jordan River in the year 29 C.E, John saw that sign. The Bible tells us what happened : "After being baptized, Jesus immediately came up from the water; and look! the heavens were opened up, from the water; and look! the heavens were opened up, and saw God's spirit descending like a dove and coming upon him. Look! Also, a voice from the heavens said: This is my Son, the beloved, whom I have approved." ( Matthew 3:16, 17) When John saw and heard this sign, he knew that Jesus was the Messiah. ( John 1:32- 34) On that day, when Jehovah poured out his spirit on him ,Jesus became the Messiah. He was the one whom God had chosen to be Leader  and King.- Isiah 55:4 . Bible prophecies, Jehovah's own words, and the sign He gave at Jesus baptism prove that Jesus is the Messiah. for more information JW.ORG

The fact of the matter: The reason why Jesus Christ our lord Jesus Christ our Lord and Savior is called the son of God, is because he is the third person in the Godhead bodily that is why he is called the son of God, just like he is also called the Lamb of God that takes away the sins of the world, the reason is only God can take away are sins.

MISUNDERSTANDING:  

1. Christ is the Son of God.2. Jesus is the son of man;3. Christ lived in Jesus as Christ can live in all. Jesus' last name wasn't Christ.