First, we call Him that because He was incarnated by the eternal Spirit and born of a virgin. In the biblical sense, the word "son" doesn't necessarily mean what it means in English as a begotten or natural-born progeny. We are "sons of Abraham" by faith and Peter called Mark his son and Paul called Timothy his son. It means something that even we can be. Just as Barnabas was known as the "son of encouragement," which his name means. Jesus nicknamed James and John "sons of thunder." That means he embodies or personifies it, not that he is in some way begotten in an abstract way.
Unfortunately, the creeds say that Jesus is begotten, not made to counter the Arian heresy and to clarify the deity of Christ. When Jesus said He was the Son of God and also the Son of Man, it meant that He embodied or personified the essence of God and man. At His trial Jesus confessed to being the Son of the Blessed One; a direct claim to being God in the eyes of the Pharisees. He is the icon of God or the express image of God meaning that all we need to know of God is seen in Him. He is the representative of God and we can know God through Him. For all the fullness of God's nature dwells in Him bodily (cf.Col. 2:9). Remember, God is spirit and invisible, to know God and see Him in glory, we must behold Jesus! "The Son is the radiance of God's glory and the exact representation of His nature..." (cf. Heb. 1:3).
Jesus was always the Son of God and didn't become the Son of God at some point in time or He would not be eternal and then He couldn't be God. But He is God in the flesh and only in His humanity was there a beginning or incarnation. Nothing that begins can be eternal and must have a cause but God is the First Cause meaning He needs no agent and is not contingent or dependent upon anyone or anything. Jesus is co-equal with the Father and sees the Father as a father figure or role model in a sense that defines His relationship with Him, not that He was born of God.
The Muslims are right in that they say God never had a Son. Jesus was and is the Son and always was from all eternity. He didn't become the Son. Muslims fail to see that the Father and the Son are One in essence, will, and attributes and this doesn't violate the law of noncontradiction. To say God is one and to say Jesus and the Father are One is not a contradiction. To say God is one and to say that God is personified in three manifestations is not a contradiction either. In one sense, God is one; in another, He is three--that is no contradiction according to the law of noncontradiction. Which lawl states: A cannot be A and non-A in the same sense at the same time.
We are sons of God in that we bear His image and represent God and are adopted into His family which the angels are not! We are privileged joint-heirs. We can be the image of God to people and manifest what God is like as witnesses and give a testimony that brings glory to God. Our purpose when is to glorify God! A Son glorifies and brings honor to a Father. In the beginning, both the Father and the Son enjoyed equal glory from all eternity.
Since Jesus is the Son of God, to worship Him is to worship God, to honor Him is to honor God, to deny Him is to deny God, to blaspheme Him is to blaspheme God, to receive Him, is to receive God, and to reject Him, is to reject God. Jesus is God in other words and for all practical purposes. We must conclude that the world may be looking for a song to sing and a creed to believe or a calling to find but they must realize that Christianity is about a person to know. Without Him in your heart, you just going through the motions and are empty inside. We must have the Son in our hearts and radiate His glory. We miss the boat if we don't realize who the Son is and what that means and should mean to us personally. We fail at our spiritual potential. Soli Deo Gloria!