If you don’t question the Septuagint... you might be a Catholic... as most of your Protestant brothers discount the inclusion of the Deuterocanonical books in the OT.
I applaud your understanding of John 1, I hope and pray it extends to John 6 as well.
Deuteronomy 4:2 Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the LORD your God which I command you.
Repeated again Deuteronomy 12:32; Proverbs 30:5-6; Jeremiah 23:28-40; Ezekiel 2:5-7; and John repeated again for those who ignore the prophets Revelation 22:18-19.
Of course John 6 was 'given' by the Heavenly Father, as even Christ Himself specifically stated in John 6:35-37 comes from the Father not Peter, an object, church, or anyone else ... Christ said All that the Father giveth Me shall come to Me; and him that cometh to Me I will in no wise cast out....