Satan is the accuser of the brethren, in general (
Revelation 12:10), but Jesus was speaking specifically to "the Jews," established in
verses 10-18 of John 5 saying, ironically, that he (
Moses) in whom they had put their hopes was their accuser because their efforts to improve upon his writings by adding cumbersome, carnal, hedging requirements (
instead of accepting the heart change that is prescribed by texts like Deuteronomy 5:29 and John 3:1-15—which Christ marveled that Nicodemus didn't understand, being a teacher in Israel) was actually doing the opposite of what they intended and making them guilty under the law they had deceived themselves they revered so much. They had no inward circumcision of the heart (
Romans 2:29) and therefore could not keep the two great commandments (
Matthew 22:36-40) which define the self-sacrificing, other-centered love from which the Ten Commandments hang and, by extension, every word that proceeds from the mouth of God.
Hope this isn't too convoluted. :)

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