Jesus was not disturbed by the negative opinions that these unbelieving Jews held of Him (5:41). He knew He would not secure the praise of all men--or even many of them. But, that was not His concern since His kingdom was not physical but spiritual in nature (cf. 18:36). Jesus wanted these men to believe on Him for their own good, but, in the next verse, He reveals why they won't do this.
"You do not have the love of God in you" (5:42). Jesus knew that these men were insincere in their attitudes. They really did not love God, in spite of their claims of loyalty.
For Jesus to come in the Father's name was to come by His authority (5:43). Jesus was the agent of the Father in coming to the world to make salvation possible. His actions were, therefore, the actions of His Father through Him. If the Jews really believed in and had regard for the Father, then they would have accepted Jesus as the Messiah. Their rejection of Christ was thus the rejection of the Father in whose name He came. Their perversity of heart was further evidenced by their disposition to accept false messiahs and to reject the only true one (cf. Acts 5:36,37).
Tragically, these Jews preferred the praise and honor which comes from men rather than the approval of God (John 5:44). Their lives were motivated by pride and worldliness (cf. 12:42,43). Until they changed, it would not be possible for them to truly believe and be honored by God.
The meaning of Jesus' words in 5:45 seems to be this: "Don't think that it is necessary for me to establish what I have said regarding you by an accusation against you before the Father; this has already been done by Moses. The one whose law you claim so strongly to respect is the one who condemns you."
WITNESS #6: MOSES
The Father also testified of Christ through Moses. Moses wrote of Jesus specifically in Deuteronomy 18:15-18, and he also wrote of Him in a typological way throughout the Pentateuch (e.g., the Passover lamb, sacrifices, bread from heaven, the bronze serpent, etc.; cf. the book of Hebrews). These Jews were guilty of rejecting Moses and his testimony. To truly believe Moses was to believe Christ, because his writings, along with the rest of the Old Testament, logically led one to Christ (Gal. 3:24). As a side note, it should be observed that this verse easily proves that Moses is the author of the Pentateuch (i.e., the first five books of the Old Testament), even though so-called scholars of today often try to deny it.
Jesus' question in John 5:47 is powerful and quite applicable today as a warning. How can someone rationally believe Jesus' words if they do not accept the writings of Moses? To reject Moses (e.g., even just Genesis 1-11), will ultimately result in rejecting Christ. How? Because if Moses was wrong, Christ must also be wrong too, since He referred to Moses' writings as true. But, of course, Moses was not wrong! The Old and New Testaments are linked together in such a way that to reject one is to logically reject the other--or at least to cause one to study with veiled eyes (cf. II Cor. 3:15,16).
This confrontation between Jesus and the religious leaders began with an attempt to convict Jesus of violating the Sabbath law as taught by Moses. Interestingly, it ended with Jesus convicting them of rejecting the law and the lawgiver on whom they based their hope!
In summary, to reject Jesus is to reject the testimony of: (1) Jesus Himself, (2) John the baptizer, (3) Jesus' works, (4) the Father, (5) the Scriptures, and (6) Moses. All of these witnesses testify to the fact that Jesus is the Son of God and that He has the divine right, as does the Father, to "work" (i.e., do good) on the Sabbath.