Isaiah 44:6; “Thus saith the LORD the King of Israel, and his redeemer the LORD of hosts; I am the first, and I am the last; and beside me there is no God.”
The expression “thus saith the Lord” or “the Lord spake” and similar phrases occur some 560 times in the Pentateuch, some 300 times in the historical and poetic books, 1200 times in the prophets and 24 times in Malachi alone. “Thus saith the Lord” appears 413 times in the Bible.
The last prophet to use this phrase was John the Baptist and you’ll notice that in the NT there isn’t one single time where the apostles or any of Jesus’ disciples used the phrase. Rather when we read scripture we see the term “the Holy Spirit says…” or the variants of this – Acts 13:2, 21:11. That’s not to say that Jesus didn’t use the phrase. In fact He used it in Luke 24:45-46 when He reminded the disciples of what had been written in scriptures.
Spurgeon defined it this way;
“Thus saith the Lord “—this is the motto of our standard, the war-cry of our spiritual conflict,—the sword with which we hope yet to smite through the loins of the mighty who rise up against God’s truth.”
The phrase “thus saith the Lord” and its derivatives means by God’s express authority. The word thus means here now and saith in Hebrew is amar, meaning to call, certify, command.
What the Lord said is forever. He doesn’t change, He doesn’t make amendments or abridgements – it’s there and done.
When Brigham and friends say the gods exist we can know it’s totally contradictory to what God has definitively said in His word. He is the Only God and there is no other.