Commentaire sur Jonas 3:2

what I tell you: and that is what Jonah later said, that in forty days Nineveh would be overturned. It wasn't necessary to spell that out here, because it is obvious.

Why did God change this time to say, "and proclaim to it what I tell you", unlike what God said the first time?

Go at once: this time, the Ninevites' decree had already been sealed. As a result, God no longer said merely that "their evil has come before Me". God sent him on the path of prophecy to tell the Ninevites what had been decreed for them, that Nineveh would be overturned in forty days.