The Torah promises reward for those who follow along the path of the prescribed Mitzvot. The expression the Torah uses is IM BECHUKAI TELECHU, “If you walk in my commandments…”.(Lev. 33,3) Obviously the meaning is if you follow my commandments. Why is the term “walk” used?
An answer once given is that one should not stand still in his practice of performing Mitzvot. He should not remain at the same level at all times. Rather, he should be moving forward always, trying to improve his way of implementing them. He should also be ever ready to move up to performing more Mitzvot to which he never paid attention previously. He should not stagnate in doing Mitzvot perfunctory but should be moving along to better and more sincere ways of performing them.
Perhaps this is what Rashi means when he states in connection with these words that we should be AMELIM or “toiling” in the performance of the Mitzvot. He should be extending himself and work hard to try to improve his method of doing the Mitzvot.