At the beginning of the John's gospel, it is announced that Jesus was God (John 1:1).
This was news, unbelievable news, that would take a whole lot more than a mere proclamation can provide in order for someone to believe it. That's why John kept writing (John 20:31).
And as he kept writing, he methodically tells stories that demand a choice from the reader. Believe or don't believe.
His stories first ask you to believe that Jesus is uniquely special, altogether superior to other spiritual powerhouses (John 1:27).
They then invite you to believe in a Savior Jesus, one who can make up for our sin (John 1:29).
They quickly challenge you to believe in the Jewish Jesus, the Messiah spoken of for centuries (John 1:45).
John then makes the reader decide whether or not he will accept Jesus as the very Son of God (John 1:49).
The rest of the stories are both evidence of these claims, but they are also whispers of yet another. It's a claim that would be the hardest to swallow of all, but also the most incredible and impactful.
It is not until the end of his book that he finally and forcefully makes the reader choose, through a resurrection appearance to Thomas (John 20:26-28), whether you will believe that Jesus is...
...God.