The 189th mitzvah is that we are commanded to constantly1 remember what Amalek did to us, i.e., to be the first to attack us [after we were redeemed from Egypt]; and to speak of it constantly; to arouse people to wage war against them and hate them, in order that it not be forgotten or the hatred towards them lessened with the passage of time.

The source of this commandment is G‑d's statement2 (exalted be He), "Remember what Amalek did to you. [Do not forget.]"

The Sifri3 says, "The phrase, 'Remember what Amalek did to you,' refers to doing so verbally. The phrase, 'Do not forget,' means in one's heart." This means that one should say verbally words that cause people to keep this hatred in their hearts. The Sifra4 says, "From the verse, 'Remember what Amalek did to you,' you might think it means in your heart. But when it says, 'Do not forget,' that means in your heart! How do we explain the commandment to 'remember?' It means to speak about it verbally." You can see how the Prophet Shmuel went about fulfilling this commandment: first he remembered them [verbally] and then commanded that they be killed. This was done when he said,5 "I remember what Amalek did to the Jewish people when they came up from Egypt."