In John 20:24-31, Thomas first doubts and then believes after he sees Jesus. In verse 29 we are told blessed are those who have not seen and yet believed. In verse 31, we learn these things are written so we will believe and have life in His name. We are so blessed that the story of the very patriarchs of the church having doubts.
In John 21, Jesus finds the disciples going back to fishing, their old life. How easy is it for us to go back to our old life when we hit obstacles. Jesus also gives Peter 3 opportunities to state his love for Jesus right after he denied Jesus 3 times. Jesus always restores.