Behold is an attention-getter. See 1.6.

They say: In Hebrew the pronoun they is emphatic. It may be rendered as “The people” (Good News Translation) or in some languages as an impersonal “One” (Die Bibel im heutigen Deutsch). Say, according to some commentators, is best expressed as “keep saying.”

Where is the word of the LORD?: In this context the word of the LORD refers to the threats made by the LORD through Jeremiah to his people, so the question here may be rendered “Where are those things the LORD said would happen?” or “When will we see all those things the LORD threatened?” Die Bibel im heutigen Deutsch has “Where is the disaster that the Lord has threatened?”

Let it come! can also be expressed as “Let it happen!”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on Jeremiah. (UBS Helps for Translators). New York: UBS, 2003. For this and other handbooks for translators see here .