Katie was a godly woman who had a non-Christian friend named Charley. On several occasions, she had the opportunity to share the gospel with him, but all he did was respond with a "thank you" before rejecting the call to faith and repentance. After this happened several times, Katie asked Charley, "Well, what would it take for you to believe in Christ?" Charley replied, "I would have to see Jesus do a miracle with my own eyes."
Charley's sentiment is not uncommon. More than one person has held that he would believe in Jesus if he could see Him with his own eyes. Today's passage, however, indicates that this is wishful thinking. If one's heart is fully hardened against God, seeing Jesus Himself do a miracle will not be enough to cause belief.
Mark writes that Jesus, having fed four thousand Gentiles, returned to Galilee, to a town called Dalmanutha (Mark 8:10), which was likely another name for a town called Magadan. In any case, in Dalmanutha, Jesus had an encounter with several Pharisees who sought "a sign from heaven to test him" (v. 11). This was no simple request for something to confirm Jesus' identity; the language used indicates a hostile demand of our Lord to prove His claims.
Jesus responded with a deep sigh in His spirit, meaning that He was greatly exasperated (v. 12). This was a sinless exasperation, indicating that Jesus' patience had just about run out, as He anticipated the day on which wickedness will reach its highest point. On that day, God will no longer wait for judgment, and He will pour out His wrath on the impenitent (Rom. 2:5). Jesus' response, John Calvin says, was born of grief that people who had seen so much of God's work through His Son would remain so obstinate. Calvin draws this lesson: "All who are desirous to promote the glory of God, and who feel concern about the salvation of men, ought to have such feelings that nothing would inflict on their hearts a deeper wound than to see unbelievers purposely blocking up against themselves the way of believing, and employing all their ingenuity in obscuring by their clouds the brightness of the word and works of God."
The response of Jesus to those who had seen His miracles is instructive. God will not do tricks for those who will believe, let alone those who have hardened their hearts against Him. Thus, Jesus told the Pharisees that they would get no sign from Him (Mark 8:12–13). If what they had seen did not convince them, nothing would.
Matthew Henry comments on today's passage that "if [unbelievers] will not be convinced, they shall not." Nothing we can do or say can convince those who have hardened their hearts to believe in Christ. Their opposition is moral and spiritual, and only God can overcome it. We should therefore pray for those to whom we preach the gospel that they would have their hearts softened by God Himself.