Rabbi [Judah HaNassi] would say: Which is the right path for man to choose for himself? Whatever is harmonious for the one who does it, and harmonious for mankind.
Be as careful with a minor mitzvah as with a major one, for you do not know the rewards of the mitzvot. Consider the cost of a mitzvah against its rewards, and the rewards of a transgression against its cost.
Contemplate three things, and you will not come to the hands of transgression: Know what is above from you: a seeing eye, a listening ear, and all your deeds being inscribed in a book.
Pirkei Avot 2:1
Chasidic Perspective. Every mitzvah possesses infinite and finite elements. Correspondingly, every mitzvah generates an infinite reward that is unknowable and a finite reward that is knowable.
The infinite element of the mitzvah is the fact that it is the Divine will and that its performance unites the person with the Infinite G-d. From this perspective, there is no differentiation between mitzvot, since all are equally the will of G-d and therefore equally unite the person with G-d.
The finite element of the mitzvah is its unique properties and its particular refining effect on the person and creation. The reward for refining creation is finite, since creation and all that is associated with it is finite. The reward for a minor mitzvah, which refines less of creation, is less than the reward for a major mitzvah, which refines more.
Hence: Be careful with a minor mitzvah as with a major one, since you do not know the reward for mitzvot. I.e., even while focusing on and internalizing the particulars of the mitzvot--by which they are "minor" and finite--retain an awareness of their infinite element, the reward for which cannot be known.
Holtzberg Memorial Edition