Musar על דברים 4:41

2) זרוז מצוה a display of eagerness to perform the commandment. That this is a higher level of performance is based on the verse אשר יעשה אותם האדם וחי בהם, "that man should do them and live (come to life) thereby," (Lev. 18,5). It means that performance should be joyful in order that a person may qualify for this level. One way of proving this is to perform the part of the מצוה one is capable of fulfilling even if one is fully aware that one will never be able to perform the מצוה in its entirety. An example of such זרוז was Moses establishing three cities of refuge on the East Bank of the Jordan, though these would not become operative until they would be matched by three more such cities on the West Bank. Moses could have left even the first three such cities to be set aside by his successor since he was aware that he would not be alive when they would begin to fulfil their designated purpose. Compare the Torah on this in Numbers 35,14-15, and Deut. 4,41.

As to the yetzer's second contention — "Since you cannot observe the din completely, it is best to distance yourself from this [(guarding your tongue)] altogether" — you can answer: "Would I allow myself to conduct my business in this way?" For example, If someone saw me running with alacrity to "make a deal" to support myself and he asked me: "Why are you running? Do you think that by doing so you will become the wealthiest man in the whole world, like Ploni?" would I not certainly answer him: "Because I will not become like him should I 'hide my hand in the dish' and not support myself?" And if this is so with the transitory body, what should I answer for the affairs of the [eternal] soul? Because I cannot observe this trait in all its details and aspects, by means of which I could rise to eternal heights of exaltedness and holiness — [as we find in the holy Zohar, Parshath Chukath, that one who guards his mouth and his tongue merits being clothed with the holy spirit, and also shining eternally in the secreted light that no angel or [Heavenly] creature can visualize, as Chazal say and as we find in Reshith Chochmah in the name of Maharam Kordovero of blessed memory, that Rav Shoshan was shown secrets in a dream in which he saw that every hair of his beard shone with a torchlike luminescence, the result of his abstinence from idle speech] — should I, therefore, forebear from guarding my soul by guarding my mouth with all my might and not being G-d forbid, of the class of "the speakers of lashon hara" and the like, of those evil classes of which Chazal state that they do not behold the presence of the Shechinah? It is this that King Solomon, may peace be upon him, intended when he wrote (Koheleth 9:10): "All that your hand finds to do with your strength — do!" To teach us that even if it enters one's mind that he will not have the strength to complete the mitzvah in all of its details, in spite of this, he should do everything that he can do. And along these lines Chazal have said on Devarim 4:41: "Then Moses would set apart three cities," that Scripture apprises us of this [to teach us] that even though the three cities across the Jordan could not serve as cities of refuge until those in the land of Canaan had been designated, and he knew that he would not enter Eretz Yisrael, in spite of this Mosheh Rabbeinu, may peace be upon him, said: "Everything that it is in my power to do, I will do," as Rashi explains there. All this we have written, with the help of the Blessed L-rd, in explanation of what is stated in Avoth d'R. Nathan, that one should not distance himself from "a trait that has no end." As to "a labor that has no completion," this applies to [the study of] Torah, as indicated by the analogy adduced there.