The Value of Each Mitzvah:

The reason each and every mitzvah is so valuable is because every mitzvah creates a "garment for the neshama." This is seen from the verse (Koheles 9:8): "At all times, your clothing should be white." The Kli Yakar (Bamidbor 15:38) explains this to be a reference to mitzvos, which are the clothing of the soul. There is, however, a major difference between clothing for the body and clothing for the neshama. Clothing for the body is made of many threads stitched together, as one string wouldn't suffice to make an entire garment, but the clothing for the soul can even be made from one "thread", i.e., one mitzvah. This is as Rav Yochanon states (Sanhedrin 111A) that even if someone only keeps one mitzvah, he can be saved from Gehenim. The Kli Yakar writes that the reason for this is because one mitzvah leads to another (Avos 4:2). Therefore, as soon as a person does one mitzvah, he has the ability to do all the mitzvos. Even if he doesn't end up doing them all, since he had the power to do them, it is considered as if he did them.