6. The Torah obligates us to honor a kohen. For example, for birkas hamazon, it is a mitzvah to honor the kohen to lead the benching. Someone asked Reb Chaim Kanievsky zt'l, if both a kohen and his father are present at the meal, who should be honored with birkas hamazon?
The Torah states that the reward for kibud av v'em is יאריכון, that his life will be extended.
The Or HaChaim notes that it doesn't state אאריך, "I will make your life long." The Or HaChaim explains, "Perhaps the pasuk is saying that the segulah of this mitzvah is a long life, in addition to the reward that Hashem will give. Some mitzvos have wonderful segulos, in addition to the reward that Hashem established, and Hashem never revealed the reward that He will give."
Rabbeinu b'Chayei (Kad HaKemech) writes in the name of Reb Sadya Gaon, "Sometimes parents live for a long time, and taking care of them becomes a burden on their children. Therefore, the Torah rewards kibud av v'em with longevity. This means, 'Honor your parents....and don't be upset that they are living so long, because then you are being upset about your own life." (The longer the parents live, the more kibud av v'em you will perform, and the longer you will live.)
