RAV KOOK ON PARSHAS BESHALACH PART 2

Translated and abridged by Rabbi Chanan Morrison Parshat Beshalach Amalek attacked the Israelites at Rephidim, intentionally targeting the weak and those lagging behind. Joshua engaged Amalek in battle, successfully defending Israel against this merciless enemy. Then God instructed Moses: "Write this as a reminder in the book, and recite it in Joshua's ears: I will completely obliterate the memory of Amalek from under the heavens." (Ex. 17:14) Why did God command Moses to write down His promise to obliterate Amalek in the Torah? And why did Joshua need to be told verbally? Couldn't Joshua just read what was written in the Torah?