Rabbi Shimon said that King David did not have a life at all, except that Adam HaRishon gave him seventy years of his own. Another interpretation: Each of the forefathers, Abraham, Isaac, and Joseph, gave him of their lives. Isaac did not give him because he comes from his side, from the left side. That is, “left” is called “darkness,” as it is written, “Abraham begot Isaac” (The Zohar, VaYishlach, Item 54).
Accordingly, we should ask why Isaac had life and it is not said that he needed to take life from Abraham’s number, as David took life from their number, and with Isaac, it is to the contrary, that he was included with Abraham and has more than Abraham.
In the work, we should interpret that when a person walks on the right, he has vitality because “the blessed cling to the Blessed.” This is not so with the left. For this reason, we must always walk on the right, and only a little bit on the left.