1-5 In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things were made through Him, and without Him nothing was made that was made. In Him was life, and the life was the light of men. And the light shines in the darkness, and the darkness did not comprehend it.
11-12 He came to His own, and His own did not receive Him. But as many as received Him, to them He gave the right to become children of God, to those who believe in His name:
14 And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth.

The essence of John's gospel is found in these few verses. He wrote specifically to show that Jesus was the Son of God. The answer is found here, while the explaination is found within the book using a number of illustrations (often numbering seven). Here we see that Jesus was before the foundation of the world - he was deity, and the world's creator (see also Colossians 1). Thus he was God (not a god, as some would have it) - the evidence is that Jesus was the Word of God (v1 & 14) who became flesh. He left his heavenly abode and has manifested the glory of God by revealing two things about God the Father: His grace and His truth. We see and hear God the Father through the words of Jesus. The word of God personified in Jesus is His divine self-revelation. We see the character and qualities of the Father expressed through Jesus (If have seen me, you have seen the Father John 14:9). Thus we are assured, that although Jesus was distict from God, he was fully God (John 10:30).

See also: Thomas L Constable, Notes of John, 2025. See < https://www.bibleportal.com/commentary/expository-notes-of-dr-thomas-constable >