John Gill Commentary Jeremiah 27:4

"and give them a charge unto their masters, saying, Thus saith Jehovah of hosts, the God of Israel, Thus shall ye say unto your masters:" — Jeremiah 27:4 (ASV)

And command them to say to their masters

The prophet is sent with authority, and ordered to speak in a very high strain, having his orders from the King of kings and Lord of lords; a greater master than those messengers had; and to enjoin them to tell their several masters in his master's name; as follows:

thus says the Lord of hosts, the God of Israel ;

who, though in a peculiar manner the God of Israel, yet was Lord of the whole world, and had all the armies of heaven and earth at his command, to enforce his power and authority; wherefore what he says ought to be attended to:

thus shall you say to your masters ;

deliver to them the following words of the great Jehovah.