A "marvelous thing" in the Bible is something that generates awe or wonder. Sometimes it refers to a miracle, but more often to something very unexpected and remarkable.
But the most marvelous thing of all is that unbelievers still persist in their unbelief. In our text passage the Lord Jesus Christ had just performed one of His most amazing miracles of creation--making perfect eyes for a man with no eyes, blind from birth. As the man testified to the frustrated Pharisees: "Since the world began was it not heard that any man opened the eyes of one that was born blind" (John 9:32). Yet these religious intellectuals, so opinionated in their prejudices, refused to believe what they saw and heard. Similarly, "when the chief priests and scribes saw the wonderful things [i.e., `marvelous things'] that He did, . . . they were sore displeased" (Matthew 21:15).
There are none so blind as those who refuse to see. One of the saddest verses in the Bible is John 1:10: "He was in the world, and the world was made by Him, and the world knew Him not." And: "He came unto His own, and His own received Him not" (v.11). Even when He raised Lazarus from the dead, "the chief priests consulted that they might put Lazarus also to death; Because that by reason of him many of the Jews went away, and believed on Jesus" (John 12:10-11).
Modern "intellectuals" are still the same, rejecting the overwhelming testimony of the created complexity in the cosmos to the fact of a personal Creator in favor of an impossible scenario of chance origin. "Herein is a marvelous thing!" Such people "willingly are ignorant" and "without excuse" (II Peter 3:5; Romans 1:20). HMM