"And he did not do many mighty works there, because of their unbelief." - Matthew 13:58
On a more temporal level, a physician or counselor can only accomplish as much as the patient believes can be done. Belief is what carries someone through the most difficult procedures and necessary prescriptions. Belief enables one to see beyond the impossibilities and move forward in hope. But unbelief is devastating.
For the passage at hand we see our Lord Jesus, the very Creator and Sustainer of the universe not doing mighty works in his own hometown. As a carpenter and tradesman he had provided for family and friends successfully for years. But now, when he came as a spiritual power and presence, the community was offended. Suddenly confidence and acceptance slipped away. Unbelief was devastating.
This subject remains an issue throughout life as we read in James 1:6-7, "But let him ask in faith, with no doubting, for the one who doubts is like a wave of the sea that is driven and tossed by the wind. For that person must not suppose that he will receive anything from the Lord" As we begin our walk with God through belief in His Son, so we must walk by faith (Hebrews 10:38) if we ever expect to see mighty works. Unbelief is devastating.