Many walked away from Jesus in unbelief and some stayed, but among the 12 that stayed there was one who didn't believe even though he fit all the descriptions of a believer.
God's sovereignty doesn't negates man's responsibility. Jesus calls us to believe to be saved, that is a part of His sovereign plan and believing is our responsibility.
What do you do when you have a Sovereignty Crisis and you are with those that believe, but not sure if you are a believer?