From the book The Gospel of John Original Version , Volume 2, translated by James David Audlin.

Traditional dogma-based interpretations of [John] 5:18 wrongly assume Jesus is declaring himself the Son of God, divinity incarnate, and that the Pharisees reject this assertion as blasphemy. Judaism is a strictly monotheistic religion, and though equating oneself with God is usually considered at least inappropriate it is never declared outright blasphemy Jesus never strays from strict monotheism in this gospel.

Jesus does say he and the father are one (17:22), but the context makes it clear that the goal is for all humanity also to be one with God and with each other (17:20-23). And this is not a oneness of identity, but a oneness of unity and commitment, as when an entire people are one in spirit and will. This indeed is the Jewish concept of covenant: for example, just as a husband and a wife remain separate persons in terms of individual identity but “become one flesh” in terms of unity and commitment (Genesis 2:24), Jesus was in the same way one with God and wanted all humanity to join him in such commitment. Even Paul gets close to this understanding in Romans 12:4-5.

James F. McGrath (NTS, 1998) says standard translations are wrong to render [the Greek] as “therefore”; he properly reads it as a concessive particle: Jesus claims God as his father yet at the same time (not “therefore”) he makes himself equal with God. Thus, McGrath concludes, the Pharisees are not challenging the God’s-son claim; rather, they are saying Jesus is no dutiful son because he presumes to usurp the unique prerogatives of God his father, making himself equal to his father, rather than being deferential and respectful toward God as a son should be. This accusation, McGrath continues, is based on the fifth commandment in the Decalogue (Exodus 20:12), and probably Deuteronomy 21:18-20, where a “stubborn and rebellious son” is one who “does not obey the voice of his father and the voice of his mother” (who form together the image of Elohim of which Jesus is claiming to be son). Indeed, such a son should be accused before the village elders as “a glutton and a drunkard” (Jesus is so accused in Luke 7:34), who must then condemn him to death by stoning. I think McGrath is right, and Jesus is here not being accused of equating himself with God but usurping God’s prerogatives, and so they may have demanded his execution as required by Leviticus 24:16. Note that Jesus emphatically answers this accusation, and not that of claiming to be God, in the subsequent verses.