What is the essence of Hashem's words?
Rashi: You need not request help from the strength of Egypt and waste your money. You will be saved with serenity and comfort, without any toil, if you will listen to Me.
Malbim: Hashem wanted to make a foundation for you, but you did not want.
What is "b'Shuvah"?
Rashi: It is an expression of rest. The same applies to "Shuvah Hashem Rivevos Alfei Yisrael" (Bamidbar 10:36). Radak - it is the same as Nachas.
Malbim: Refer to 30:15:3:2.
After saying "b'Shuvah va'Nachas", why does it add "b'Hashket uv'Vitchah"?
Radak: The matter is repeated in different words.
Malbim: There are two ways to be saved from the enemy. (a) Only he will be saved. (b) He will overpower the enemy and defeat it. If you want, you will be saved b'Shuvah va'Nachas; you will not do anything, just rely on Hashem. If you want a higher level, to overpower the enemy with strength, this requires "b'Hashket uv'Vitchah" - strong trust in Hashem, also in the heart and Nefesh.
What will be their Gevurah?
Radak: They will dwell in their cities. "Hashem will fight for you" (Shemos 14:14).
