The eating of matzah is called michla d’asvasa—the food of healing. Eating matzah on pesach is considered medicine for the soul. Just as with physical medicine the prescription is not the same for everyone, so too the healing for the soul is not equal for everyone and each of us receives a different prescription.
For some it is sufficient to eat matzah on the night of the Seder only, and they ingest enough kedusha to last them the whole year. Others of us must eat matzah all seven days of Pesach for the same effect.
(מאור ושמש הפטרה לפסח)