What does John 5:31 mean?

According to Jewish legal procedure, a person could not testify alone on their own behalf. A creative liar can make up anything. Nor could a single witness establish facts, for the same reason. Rather, in a courtroom setting, two or three witnesses were required (Deuteronomy 17:6; Numbers 35:30). Later in this gospel, Jesus will make the point that some facts only He can relate to (John 8:14). In this context, however, the claims He is making can be verified by normal means; therefore, it's reasonable to provide evidence.

This passage is extremely important in discussions of biblical faith. Jesus makes no appeal to "blind faith." He does not tell the Pharisees to believe "because I said so." Nor does He dismiss the need for evidence. Rather, He provides reasons why faith in His message is reasonable. Jesus will fulfill the normal human requirements of evidence, by giving three separate lines of evidence to prove His claims.

These three categories are human testimony, in the form of John the Baptist (John 5:33); observations, in the form of Jesus' miracles (John 5:36); and Scripture (John 5:39). Jesus will use these arguments to complete His response to Jewish authorities persecuting Him for claiming to be equal with God (John 5:18).