John’s purpose in this passage of scripture is to convince us that Jesus is the Son of God, is himself God, and therefore equal to God the Father and God the Holy Spirit in power and glory. Jesus is fully and completely God. We should believe that Jesus must be God, since he does the things that only God can do, he judges men as only God can judge, and reliable witnesses reveal to us that he is God.
Jesus infuriated the Jewish leaders by saying “My Father is working until now, and I am working” (John 5:17). One the one hand, Jesus makes a distinction between himself and God the Father. One is the Father, the other the Son. On the other hand, it is also true that they are both God. God the Father ceased his work of creating on the sixth day, but this does not mean that he ceased working altogether. He always works by sustaining the universe by his power. Without him the entire universe would cease to be (Acts 17:28). God the Son shares in this work, for if the Son quit working everything would disappear. This makes him equal with God the Father. Indeed, Jesus cannot act in independence from God the Father. He can only do the things he sees his Father doing, and whatever the Father does the Son does also. Jesus is saying, in effect, “Whenever you see God do anything, I am also doing it.”
Jesus had already said enough to make the Jews mad with him, but he goes much farther. He claims to be the perfect and righteous judge of all mankind. The Old Testament taught that God is the one that raises people from the dead and gives them live (Deut 32:29; 1 Sam 2:6; 2 Kings 5:7) and the one who judges their sins (Gen 18:25; Judges 11:27; 1 Sam 2:10; Psalm 67:4). Jesus claims to be the judge and the one who gives spiritual life. He is the one who will raise their bodies from the dead as well. Eternal life is given only to those who trust in him, not to those who reject his deity like the Jewish leaders who were standing before him.
Finally, Jesus tells the Jewish leaders that God has sent them reliable witnesses concerning him. In Jewish courts, there always had to be two or three witnesses concerning any matter (Deut 19:15). Thus Jesus invites the Jewish leaders to an imaginary courtroom in which several witnesses testify to his deity. God the Father has testified by sending John the Baptist and by giving men the Old Testament, which speaks of Christ. John the Baptist also testified about Jesus’ deity, calling people to believe in Jesus. Jesus’ own works testify to his deity, since he displays the power of God as he works miracles. Scripture testifies to him, by pointing people to him. Last, Moses testified to him, and if the Jews had really known anything at all about Moses, they would have accepted him as the Messiah.