What is the meaning of "va'Yishlach Hashem Es Yado"?
Rashi: Every Shelichus regarding the hand means extending it.
Rashi citing Targum Yonasan: Hashem sent His words of Nevu'ah.
Radak: He sent the angel that appeared to Yirmeyah and spoke to him in the name of Hashem, and was called by Hashem's name. Yirmeyah saw a Nevu'ah that he stretched his hand to him, and the words touched his mouth.
Malbim: Shelichus Yad regarding Nevu'ah is giving power to carry out something. Yad Hashem is a metaphor for power to fulfill. Chezkas Yad is power to uproot, plant, destroy or build.
What is the meaning of "va'Yaga Al Pi"?
Radak: The words touched his mouth. It seems that something tangible touched his mouth to fix it to speak without fear. It says also about Yeshayah (6:7) "va'Yaga Al Pi" - the coal touched his mouth. There is a Patach under the Yud; it is Hifil.