Musar su Numeri 35:14

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.