The second aliyah discusses aiding our neighbor when we see his animals running away or under a burden.
The aliyah ends with the mitzvah of sending away the mother bird when we take its chicks or eggs, and the reward is specified as a long life. Since the mitzvah of honoring one's parents has the same reward of a long life, it's been said that this mitzvah, the chasing away of the mother bird, the easiest mitzvah, and honoring one's parents, what some consider the hardest mitzvah, both have the same reward. Therefore we can conclude that it this also the reward for every mitzvah in between.
