But the disciples' fear really betrays their doubt - even doubting what their eyes behold. Thomas is not the only doubter in the crowd. Generally, dead people stay dead - so their doubting may not be all that incredible. In fact, what their doubting affirms is that Jesus did, in fact, die on the cross. But their doubting is also an unfaithful concession that death, and the law that condemns, have the last word.
Death is tangible, concrete.
So the qualifying limitation on the heart of the disciples is that their messianic hope in Jesus is a dashed vision, an illusion of what might have been. It is not faithful, or hopeful. Adding to the woes of the doubting disciples is the equally reasonable conclusion that, if death and the law's condemnation reigns, so does the God who upholds that judgment on transgressors of the tradition. They are condemned for violating the tradition of the law in considering themselves disciples of Jesus, but they also betray their Lord in their doubting. No locked doors can bar that judgment.