יד. וַיֹּאמֶר יְ־הֹוָ־ה אֶל מֹשֶׁה כְּתֹב זֹאת זִכָּרוֹן בַּסֵּפֶר וְשִׂים בְּאָזְנֵי יְהוֹשֻׁעַ כִּי מָחֹה אֶמְחֶה אֶת זֵכֶר עֲמָלֵק מִתַּחַת הַשָּׁמָיִם
Why does Hashem command us to write and to say in the ear wouldn't one be enough that it not be forgotten?
Reb Chaim Volshoin Answers based on the Gemara in Baba Basra that Yoav did not kill out the Female Amalakim because he HEARD "תמחה את זכר עמלק" that is Kill out the MALES of Amalek but really the Vowelazation means the Memory hence you have too say into the ear and write it because if not it will lead to these types of erors.