Here is a practical lesson from this account: a positive response to Jesus should never be taken as proof of authentic trust in Him. There is a shallow, fickle brand of “belief” that is not saving faith at all. From the first public miracle He performed until this very day, there have always been people who “accept Christ” without truly loving Him, without submitting to His authority, and without abandoning their self-confidence and trust in their own good works. That is precisely what John describes at the end of John 2, and that becomes his transition into the Nicodemus narrative. Nicodemus was (at this point) one of those almost-believers to whom Jesus did not automatically commit himself.
John makes a clever play on words in the closing three verses of chapter 2. The expression “many believed in His name” in verse 23 and the expression “Jesus did not commit Himself unto them” in verse 24 both use the same Greek verb. John is saying that many people responded to Jesus with a kind of enthusiasm that fell short of whole-hearted faith, so He didn’t completely trust them, either. In other words, they said they believed Him, but He didn’t believe them. He had no faith in their faith.
From: The Jesus You Can’t Ignore: What You Must Learn from the Bold Confrontations of Christ by John MacArthur (Nashville: Thomas Nelson, 2008), pp. 54-55.