What is the meaning of "sha'Atah"?
Rashi: It is like she'Atah. Radak - there is a Kamatz under the Shin in order to extend the Aleph.
Why did he need a sign about Who speaks with him?
Malbim: If it is Hashem Himself without an intermediary 1 , it will be a miraculous salvation which does not need a big army. If an angel speaks with him, the salvation will be through natural means with a big army and war.
I.e. Hashem Himself dwells in the angel. If not, the angel is an intermediary.
Why did he say "Im Na Matzasi Chen b'Einecha"?
Malbim: This is like Moshe said "Im Matzasi Chen b'Einecha Yelech Na Hashem b'Kirbeinu" (Shemos 34:9).
What Os did Gid'on ask Hashem to do?
Malbim: Even if Hashem will let him offer a Korban, which proves that it is Hashem (refer to 6:18:1:1), Hashem's promises to an individual can be canceled. Yakov was worried lest sin cause Bitul of Hashem's promises to him. However, if an Os accompanies the promise, it is unconditional. Gid'on requested that Hashem accept the Korban miraculously, for an Os.
