God told Israel, “You didn’t believe Me when I said you had nothing to fear, that I would fight for you. You completely forgot that I bore you up like a child and cared for you. You never did trust Me, even though I went before you, gave you a cloud to shelter you from the blazing sun, gave you a fire by night to light your way and bring you comfort in the black night. Instead, you voiced your doubts, slandered Me, and made Me out to be a liar” (see Deuteronomy 1:27-35).

You can be saved, Spirit-filled, and walking holy before God, yet still be guilty of unbelief. You may think, “I don’t have any unbelief.” But do you get upset when things go wrong? Are you fearful of failing God? Are you restless, afraid of the future?

The believer who has unconditional faith in God’s promise enjoys complete rest. What characterizes this rest? A full, complete confidence in God’s Word, and a total dependence on His faithfulness to that Word. Indeed, rest is the evidence of faith.

You may wonder: How does a believer’s heart become hardened in unbelief? We see a shocking illustration in Mark 6. The disciples were in a boat headed for Bethsaida, sailing in the darkness. Suddenly, Jesus appeared, walking on the water. The twelve thought He was a ghost and shook with fear. But Christ assured them, “Be of good cheer: it is I; be not afraid” (Mark 6:50). Then He stepped into the boat, and the wind ceased.

The next verse says everything about the disciples’ hearts in that moment: “They were sore amazed in themselves beyond measure, and wondered. For they considered not the miracle of the loaves: for their heart was hardened” (6:51-52). (The Greek meaning of hardened here indicates “stone-like, blind, stubborn disbelief.”) We are being reminded that these men had just experienced an incredible miracle. They had seen Jesus feed five thousand people with only five loaves and two fishes and He had used the twelve to do it. When Mark tells us the disciples “considered not” this miracle, he means, “They couldn’t put it all together.”

Hardening comes when you take the super out of supernatural. These men didn’t have the faith to believe what they’d just seen Jesus do. Within twenty-four hours, they had dismissed His miraculous feeding as some kind of natural event. They still had doubts about Christ’s supernatural power.