The verse cited originally continues: "I shall fill the number of your days." This is the advice given to prevent feelings of self-satisfaction from arising. To explain: When a person contemplates that he has been given a fixed number of days, as implied by the verse:1, 2 "Days were created," i.e., every person has been given a fixed number of days, no more and no less, then every day, every moment, and every hour, he must carry out his Divine service to fulfill his mission in this world.3 He is anxious about this, [so anxious that] he has no opportunity at all to think about matters [like his own] spiritual level.

To cite an example: [Before he passed away,] Rabbi Yochanan ben Zakkai told [his students]: "I don't know on which path they will lead me."4, 5 [Now, why would Rabbi Yochanan be in such a quandary?]

Among the resolutions offered: Rabbi Yochanan was so preoccupied with the fulfillment of his mission that he did not have a chance to think about his own spiritual level. He was so dedicated, anxious, and preoccupied with the fulfillment of his mission every day, every hour and every moment, that he was not aware of what was happening with his own intellectual or emotional powers. Certainly, he [was not aware of the state of] his hidden soul powers.6

How much more so [does such a concern apply with regard to an ordinary individual]! He should have no feelings of self-satisfaction, because he knows that he must fulfill his mission every moment. If one moment passes in which he is not carrying out his tasks, then not only has he failed to use an opportunity that has been granted him to flourish in his Divine service, he has rebelled against G‑d, King of kings, in failing to fulfill the mission with which he has been charged.

As a result of contemplating this, not only will a person have no feelings of self-satisfaction — [represented by the words "in your land" (in the above verse) — on the contrary, were someone to ask him, "What is happening with your 'land'?" i.e., your will, he will bitterly call out: "Do I care about my will? Do I care about pleasure? About love? About fear?" How can he think about spiritual levels when at every moment he must be on guard to ensure that not one moment will pass in rebellion against the King by failing to fulfill the mission [demanded of him] at that particular time!7

When a person carries out the charge: "There will not be a woman who loses her young or who is barren in your land," i.e., he does everything possible to see to it that, as explained previously, his Divine service will be characterized by genuine love and fear and that it will continue and thrive as a result of his lack of self-satisfaction,8 he is promised [blessings] from Above: "There will not be a woman who loses her young or who is barren in your land…."

Summary

Feelings of self-satisfaction can be prevented from arising by contemplating that every person has been given a fixed number of days — no more and no less — and that every day, every moment, and every hour must be used to fulfill his mission in this world. When a person contemplates this, he will be preoccupied with the fulfillment of his mission and will not have a chance to think about his own spiritual level.

In this way, he will carry out the charge: "There will not be a woman who loses her young or who is barren in your land," i.e., he will enable his love and fear to continue to thrive. As a result, he will receive truly ample blessings from Above.