Albert Barnes Commentary Jeremiah 1:9

"Then Jehovah put forth his hand, and touched my mouth; and Jehovah said unto me, Behold, I have put my words in thy mouth:" — Jeremiah 1:9 (ASV)

Touched - "Made it touch." This was the symbol of the bestowal of divine grace and help, by which that lack of eloquence, which the prophet had pleaded as a disqualification, was removed.