And thou shalt say unto Pharaoh, Thus saith the LORD… – Exodus 4:22

“Thus saith the Lord” is that with which we must confront the Lords enemies. When Moses went in before Pharaoh, the words which he used were not, “The elders of Israel have consulted, and thus have they bidden me say,” not “Our Father Abraham once said, and his words have been handed to us by long tradition”-such talk would have been readily resisted; but he confronted the haughty monarch with “Thus saith the Lord, Let My people go;” and it was the power of this divine word which rained plagues upon the fields of Zoan, and brought forth the captives, with silver and gold. Pharaoh might boast, “Who is the Lord, that I should obey His voice?” but ere long he knew that Jehovah’s Word was mightier than all the horsemen and chariots of Mizraim and was not to be resisted without terrible defeat. To this day, if we would break sinners’ hearts, our hammer must be “Thus saith the Lord;” and if we would woo them to obedience to King Jesus, our reasons must come from His own Word. I have often noticed in conversion, that, though sometimes a particular passage of the sermon may be quoted by the converted person as the means of enlightenment, yet in the majority of cases it is the text, or some passage of Scripture, quoted during the sermon, which is blessed to do the work. McCheyne says, “Depend upon it, it is God’s Word, not our comment upon God’s Word, that saves souls;” and so it is. Let us use much of Scripture, much of the pure silver of sacred revelation, and no human alloy. “What is the chaff to the wheat, saith the Lord?” ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0591.cfm