The Jews had a weakening of faith in Hashem right after He took them out of Egypt, when they traveled without water for three days. Hashem punished them with the attack of Amalek. The mitzvah to remember Amalek, according to this medrish, is to remind ourselves to strengthen our faith when we feel we are becoming lax. If one is waning in faith, or has any difficulty, wouldn’t it be more practical to be reminded, as clearly as possible, to get back on the right track? Why not simply say: ‘Remember to strengthen your trust in Hashem when you feel you are losing it!?
Based on the context of the Rosh, we are not dealing with a onetime mistake but rather a problem with some level of frequency. The Rosh says the best way to handle it is to set a reminder of the original punishment given for the mistake. This has a greater impact on a person, to help him correct his ways, rather than to constantly be spelling out what he or she did wrong. In this case, we have a mitzvah to always remember what Amalek did to us. Some people even recite this paragraph every day with the five other events. That would seem to mean that it is very easy to lose one’s trust in Hashem and we need constant reminders to build our faith.
However, there is another practical lesson we can learn from here, which is that, as parents and teachers, the proper way to redirect children who are continuously slipping in some area is to remind them of the original punishment they received for the mishap, and that will reinforce the notion to do the right thing.