Charles Ellicott Commentary Jeremiah 16:21

"Therefore, behold, I will cause them to know, this once will I cause them to know my hand and my might; and they shall know that my name is Jehovah." — Jeremiah 16:21 (ASV)

I will this once cause them to know ... —The warning comes with all the emphasis of iteration, this once. As in a way without a parallel, once for all, they should learn that the name of the God they had rejected was Jehovah, the Eternal (Exodus 3:14), unchangeable in His righteousness. The thought is parallel to that of Ezekiel 12:15.