1)
Why does it say "none of his words fell to the ground"?
1.
Radak: Everything he said came about; Hashem fulfilled it, even things he did not say with Ru'ach of prophecy. Through this, all Yisrael knew that he is a trustworthy Navi.
2.
Malbim: Through this, all knew that he is a Navi Emes - "Eichah Neda
