The Torah states ‘ushmartem ess hamatzos’ — guard the process of making the matzos that they should not leaven. All of this, for the sake of matzos mitzva. The main requirement is only for the matza of Seder night. Holy Yidden keep this requirement for all of the matzos for Pesach. (MB2,3)
The din of matzos shmura cannot be achieved by gentiles, deaf-mutes, insane people, and children. They cannot do the required guarding from chometz. Therefore, these people should not add water to the flour, knead, shape, nor bake the dough. (ShA1 — BeH)
This mitzva of guarding the matzos from chometz while processing is greater when you do it yourself. Therefore most scholars and rabbonim come and involve themselves in the preparation of the matzos. (ShA2 — MB5,6)
It is fitting for every person to involve himself in this mitzva. If you can get yourself to sweat, it will be a great tikkun for a severe aveira. (ShA2 — MB7)
