John the beloved Apostle wrote this Gospel around 90 AD. It appears to be written to all believers to affirm that Jesus was/is God in Flesh. He quotes some scripture but mostly tells the story of Jesus and his ministry. John 20:31 and 21:24-25 summarizes what and why he wrote.
20:31 But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.
21:24-25 This is the disciple which testifieth of these things, and wrote these things: and we know that his testimony is true.25 And there are also many other things which Jesus did, the which, if they should be written every one, I suppose that even the world itself could not contain the books that should be written. Amen.
He quotes from the scripture very little, using Isaiah, Psalms, Zechariah. Listed are the direct quotes (not including what Jesus quoted) found in the Book of John.
John 1:23 Matthew 3:3 Mark 1:3 Luke 3:4 He said, I am the voice of one crying in the wilderness, Make straight the way of the Lord, as said the prophet Esaias.
Isaiah 40:3 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.
John 2:17 And his disciples remembered that it was
written, The zeal of thine house hath eaten me up.
Psalm 69:9 For the zeal of thine house hath eaten me up; and the reproaches of them that reproached thee are fallen upon me.
John 12:13 Matthew 21:9 Mark 11:9
Took branches of palm trees, and went forth to meet him, and cried, Hosanna: Blessed is the King of Israel that cometh in the name of the Lord.
Psalm 118:26 Blessed be he that cometh in the name of the Lord: we have blessed you out of the house of the Lord.
John 12:15 Matthew 21:5
Fear not, daughter of Sion: behold, thy King cometh, sitting on an ass’s colt.
Zechariah 9:9 Rejoice greatly, O daughter of Zion; shout, O daughter of Jerusalem: behold, thy King cometh unto thee: he is just, and having salvation; lowly, and riding upon an ass, and upon a colt the foal of an ass.
John 12:38-40 That the saying of Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed?
Isaiah 53:1 Who hath believed our report? and to whom is the arm of the Lord revealed?
39 Therefore they could not believe, because that Esaias said again,40 He hath blinded their eyes, and hardened their heart; that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them.
Isaiah 6:10 Make the heart of this people fat, and make their ears heavy, and shut their eyes; lest they see with their eyes, and hear with their ears, and understand with their heart, and convert, and be healed.