Charles Ellicott Commentary Jeremiah 20:9

"And if I say, I will not make mention of him, nor speak any more in his name, then there is in my heart as it were a burning fire shut up in my bones, and I am weary with forbearing, and I cannot [contain]." — Jeremiah 20:9 (ASV)

Then I said ... — The sense of a hopeless work, destined to fail, weighed on the prophet’s soul, and he would willingly have withdrawn from it; but it (the word in italics, though it does not spoil the sense, is scarcely needed) burned like fire within him and would not be restrained.

I could not stay. — A better rendering is, I prevailed not. Here again, the interpolated word is unnecessary and partly spoils the emphasis. The “I could” is the same word as “prevailed” in Jeremiah 20:7. God had prevailed against him, compelling him to undertake a work against his will, but he could not prevail against God. Like so much of Jeremiah’s language, this also came from the hymns of Israel (Psalms 39:3).