What does John 5:37 mean?
The introduction to this gospel mentioned that God the Father had never been seen directly by men. Rather, God sent Jesus to serve that purpose (John 1:18). This opening passage referred to Jesus repeatedly as "the Word" (John 1:1) using the Greek term Logos, meaning "the message, meaning, or definition." While truth is truth, no matter who accepts it (John 8:14), Jesus knows that human beings have a reasonable need for evidence (John 5:34). Rather than appealing to blind faith, Jesus provides exactly what the Jewish legal system required. Namely, three witnesses to support a claim (Numbers 35:30; Deuteronomy 17:6).Jesus first referred to human testimony, meaning John the Baptist (John 5:33). He then referenced even more potent powerful support, which is observation. In this case, it means the miracles He performed (John 5:36). Now, Jesus offers what Jewish religious authorities should think of as the most powerful testimony of all: the written Word of God.
However, this testimony is lost on Jesus' critics. According to Christ, these men have never heard the voice of God. They certainly knew the words and letters of the Law, so how is it possible that they didn't recognize Jesus? The answer is one human beings naturally reject, but which experience tells us is true: "knowledge" is different from "faith." James, for example, makes the point that merely knowing about God is different from having saving faith in God (James 2:14, 19).
In Romans, Paul points out that people come to faith through hearing the word—the gospel—of Jesus (Romans 10:17). And yet, as Jesus will point out later, a person cannot accept truth if they're already closed off to it (John 7:17). A humble attitude of obedience must come before a person can learn. The Jewish religious leaders had knowledge, but they did not have humility or true faith, so they did not recognize the fulfillment of their own Scriptures (John 5:39–40).