Jeremiah 1:9 - Matthew Poole's English Annotations on the Holy Bible

Then the Lord put forth his hand: God having before excited the prophet to his work by command and promise, doth now in a vision establish and confirm him, either by the hand of an angel, Isaiah 6:6,7, or rather, by himself in some visible shape. Touched, Heb. came upon, as the word is used, Judges 20:41, hereby enabling him to speak; or, Thou shalt be my mouth to deliver my words; partly, to let Jeremiah understand that they were God's words; and partly, to intimate that they should be effectual; and partly, that he should never be without them, but continually supplied. See the like kind of phrase Jeremiah 5:14. And he adds, Behold; q.d. Attend to what I am about to say; or, Look upon this outward sign, and let it assure thee of the thing signified.