After recording his win over Peter in the race to the tomb for all of history to read, John writes that when he saw the empty tomb, he believed. At that moment, he believed what Jesus had said about having to die and be raised up.
Later on however we read about Thomas, who wouldn't believe unless he saw the risen Jesus and could put his finger through the holes in his hands.
At times we all want to "see something" to help us believe, what we usually want is to see something big, something miraculous. But Jesus said: “You believe because you have seen me. Blessed are those who believe without seeing me.”
John's faith wasn't blind, there was evidence of the resurrection, Jesus wasn't there, but he hadn't seen Jesus yet.
In the same way, we have evidences of God at work in our own lives, sometimes we don't recognize it, like Thomas wouldn't recognize the facts and testimonies of the other disciples, but if we apply faith to them, we will see God's miracles in our own lives.