If Jesus is God, also Messiah, also Word.... and many other title....
Why Son of God?
What is the significance of using that word?
Is he actually God's son... while at the same time God.... What is the significance of being Son? What is the necessity of that title?
There are three Divine Persons: the Father, the Son, and the Holy Spirit.
The Son is called Son because He has His origination from the Father, not in time but in eternity; He is therefore God from God. Being what His Father is: God.
We use these terms "Father" and "Son" because this is the way the sacred writers wrote, and we receive as inspired of God. We should not imagine this in biological terms; but rather it speaks of begetting and begotten; of One and the Other; Generator and Generated. The Son is called Son because He is of the Father, and the Father is called Father because He is the One from whom the Son is from. Yet this generation--this begetting--is not an activity, something that has happened, rather it is an eternal reality. The Father never began to beget, nor was there ever a time when the Son was begotten; rather the Son is eternally begotten, eternally generated of the Father. The Son is uncreated, eternal, without beginning and without end--even as the Father is.
The Father and Son are, therefore, two distinct "Persons" but nevertheless one-and-same in Being. The Father is God, the Son also is God; the Son is not less God than the Father, but is God completely and perfectly even as the Father is God.
Thus it is not a "title", but a reference to Who He is in relation to the Father. He is the Son, the Eternal Son, of the Father.
In the One God there are Three Persons, subsisting in eternal majesty, equal in glory, never confused and never separated. The Father is never without His Son, neither is the Son without His Father; and neither are ever without the Holy Spirit.
St. Augustine offers us this illustration of love: Complete Love always subsists of Lover, Loved, and Love itself. Take away any of these aspects and talk of love makes no sense. Here's an example, "Jimmy loves Sally", we have here Jimmy, the one who loves; and Sally, the one that is loved, and then between them is the love itself. Take away any of these and talk of love becomes nonsense. If we say "Loves Sally" we rightfully should ask, who or what loves Sally? If we say "Jimmy loves" we rightfully should ask who or what does Jimmy love? And if we say "Jimmy Sally" we are left the most perplexed because we have no way to make sense of this at all.
St. Augustine then wants us to understand that "God is Love" is not a meaningless aphorism, but communicates something actual and real about the Divine. God is Lover, Loved, and Love--for love without a lover or without a loved is nonsense. There must therefore always be Lover and Loved and Love itself. And this we find in the Trinity: For to say God is love is to say that there is always Lover, Loved, and Love itself.
Three Divine Persons, because there is always Lover, Loved, and Love. The Father loves the Son, the Son loves the Father, the Spirit is the bond of love between Father and Son. So is the Father love? Yes, for He loves His Son--and this has always been true. Is the Son love? Yes, for He loves His Father, and this has always been true. Is the Holy Spirit love? Yes, for He is the love-bond of Father and Son, He loves the Father, He loves the Son and is loved by the Father and the Son.
Thus there is always Three, even as there is only One. Three Persons, one Being.
-CryptoLutheran