Jesus is God is more readily understood with the knowledge that in Jesus Christ is the fullness of the Godhead as the Bible says:
For in him dwelleth all the fulness of the Godhead bodily (Colossians 2:9).
Christians today can reconcile Christ to "the Son" but the true nature of Christ remains a mystery to them. Through scripture though, the truth about Jesus Christ is revealed. The Son has a dual nature - He is fully God and fully man. We will clearly see that in the following discussion.
Having said that though, the revelation of Jesus Christ comes to us from God just as it happened to the Apostle Peter:
He saith unto them, But whom say ye that I am? And Simon Peter answered and said, Thou art the Christ, the Son of the living God. And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. (Matthew 16:15-17).
We will begin this study by looking at scripture in the Old Testament that states Jesus is God and the Father. Isaiah prophesied many times that God would reveal himself as Jesus. Let us start with:
Behold, God is my salvation; I will trust, and not be afraid: for the LORD JEHOVAH is my strength and my song; he also is become my salvation (Isaiah 12:2).
The Hebrew word for salvation, from Strong's dictionary, is "yshuw`ah", pronounced "yesh·ü'·ä" or "Yeshua" which in English is "Jesus". Paraphrasing, we have,
...the LORD JEHOVAH...is become my Jesus.
You can find more discussion at Is Jesus' name really Yeshua?
The most recognized of Isaiah's prophecies is,
For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace (Isaiah 9:6),
which emphatically states that Jesus is God and the Father.
Another of Isaiah's prophecies is,
Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel (Isaiah 7:14).
and when it is lined up with the parallel scripture from the New Testament, it tells us that Jesus is God with us:
Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us (Matthew 1:23).
Isaiah tells us again that God will save us,
Say to them that are of a fearful heart, Be strong, fear not: behold, your God will come with vengeance, even God with a recompense; he will come and save you. Then the eyes of the blind shall be opened, and the ears of the deaf shall be unstopped. Then shall the lame man leap as an hart, and the tongue of the dumb sing: for in the wilderness shall waters break out, and streams in the desert (Isaiah 35:4-6).
and in the Book of Luke we find Jesus applying Isaiah 35:4-6 to Himself,
Then Jesus answering said unto them, Go your way, and tell John what things ye have seen and heard; how that the blind see, the lame walk, the lepers are cleansed, the deaf hear, the dead are raised, to the poor the gospel is preached (Luke 7:22).
Then we see that John the Baptist in Matthew 3:3 fulfilled this prophecy:
The voice of him that crieth in the wilderness, Prepare ye the way of the LORD, make straight in the desert a highway for our God (Isaiah 40:3).
The New Testament builds onto the revelation of Jesus Christ. The Apostle John knew that Jesus is God and he starts the Gospel of John with this revelation:
In the beginning was the Word, and the Word was with God, and the Word was God. .... And the Word was made flesh, and dwelt among us (John 1:1 & John 1:14).
Thomas confesses to Jesus,
..... My Lord and my God (John 20:28).
and Luke records,
...the church of God, which he hath purchased with his own blood (Acts 20:28).
The Apostles Peter and Paul knew that Jesus is God:
...through the righteousness of God and our Saviour Jesus Christ (2 Peter 1:1),
In whom we have redemption through his blood, even the forgiveness of sins: Who is the image of the invisible God, the firstborn of every creature: For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him: And he is before all things, and by him all things consist. And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence (Colossians 1:14-18),
Looking for that blessed hope, and the glorious appearing of the great God and our Saviour Jesus Christ (Titus 2:13).
Most importantly, Jesus Himself repeatedly states that He is God and the Father:
I said therefore unto you, that ye shall die in your sins: for if ye believe not that I am he, ye shall die in your sins (John 8:24),
Jesus saith unto him .... he that hath seen me hath seen the Father ... (John 14:9),
I and my Father are one (John 10:30),
I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty (Revelation 1:8), and
And unto the angel of the church of the Laodiceans write; These things saith the Amen, the faithful and true witness, the beginning of the creation of God (Revelation 3:14).
As we have seen from the Bible, Jesus is the Father and Jesus is God.
From scripture, we know that God is not a person, He is a Spirit,
God is a Spirit: and they that worship him must worship him in spirit and in truth (John 4:24).
We see this clearly elsewhere in scripture. Below when the Apostle Peter was speaking (but recorded by Luke), he equated the Holy Ghost and God:
But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land? Whiles it remained, was it not thine own? and after it was sold, was it not in thine own power? why hast thou conceived this thing in thine heart? thou hast not lied unto men, but unto God (Acts 5:3-4).
Simple deduction then defines that Jesus is the Spirit, or "Holy Spirit", "Spirit of God" and "Holy Ghost". Since Jesus is God and God is the Spirit then Jesus is the Spirit.
... I will raise him
up at the last day (John 6:44).
The Apostle Paul says,
But if the Spirit of him that raised up Jesus from the dead dwell in you, he that raised up Christ from the dead shall also quicken your mortal bodies by his Spirit that dwelleth in you (Romans 8:11), and
To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory (Colossians 1:27).
meaning that Jesus in John 6:44 is the Spirit that will quicken the mortal body in Romans 8:11 and that this same Spirit in Romans 8:11 is "Christ in you, the hope of glory" in Colossians 1:27.
Here are some other parallel verses of Scripture which further reveal that Jesus is the Holy Ghost:
God knew that He would manifest himself in the flesh (1 Timothy 3:16) as the atonement (Romans 5:11), the propitiation (Romans 3:25), the sacrificial lamb from the beginning of His Creation,
And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world (Revelation 13:8).
Up until this point in time God had the titles of "the Father" and the "Holy Spirit". As we just read, He knew He would come as our salvation but He didn't need a title to describe Himself until He came in the flesh. The instant He came in the flesh though he took on the title, "the Son".
But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law (Galatians 4:4).
As we already observed, the title the Father applies to God, the Holy Spirit and to the deity of Jesus. Since Jesus was fully human as well, the title the Father could not describe the humanity of Christ, so God needed a title for His humanity, thus the Sonship came into being when Jesus was born.
Also, the Son was begotten,
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life (John 3:16),
at a point in time, therefore Sonship is not eternal.
Jesus had a dual nature, fully God and fully man. The term Father refers to God himself, the full deity of God. Likewise the term Spirit of God, refers to the full deity of God, or the Father. That is why God the Father is Biblical,
And that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father (Philippians 2:11).
On the other hand "God the Son" is not Biblical. It cannot be correct as the Son of God refers to Christ's humanity. God or Father do not describe the dual nature of Christ. That is why God introduced the third title to describe Himself robed in flesh.
Earlier, we reconciled that Jesus is the Father and the Holy Ghost. Now it is clear why Jesus is the Son and that God the Father is not the Son. This clarity reveals the truth about Jesus Christ - He is the Father, He is the Son and He is the Holy Ghost - in Him is the fullness of the Godhead. With this revelation, the mystery of the Godhead should disappear so we can grasp that Jesus is God.