Moshe and Aharon were instructed to count Bnei Levi in a manner much different than the rest of Bnei Yisrael. Bnei Yisrael were counted once, from the age of twenty to sixty years of age. Bnei Levi, on the other hand, were counted twice. In the first census, they were counted from the age of one month and above. There was no minimum, since the thirty day old age only ensured the viability of the child. There also was no maximum age for Leviim. In the second census, the Leviim were counted according to their eligibility for service. This census had a minimum age of thirty years old and a maximum of fifty. What is the rationale for the disparities between the two cencuses of Bnei Levi and the census of the rest of Yisrael?
Horav Yosef Shaul Natenson, zl, takes a very practical approach to reconciling the differences between the countings. Members of Bnei Yisrael each achieved his distinction based upon his own merit. Thus, each had to earn his way and demonstrate his maturity and ability to go forward to represent the nation. The age of twenty years was designated as the appropriate time for acceptance in the legion of Yisrael. The merit of the Levi was inherited. He received access to the Leviah from his father. Hence, he was inducted as soon as it was clear that his birth was viable.
In order to serve in the Mikdash, however, it was essential that each Levi be especially deserving of the distinction. In fact, he had to wait until the age of thirty -ten years longer than a Yisrael waited! This teaches us an important lesson. The greater one’s yichus, ancestry, the more noble one’s pedigree, the more he is expected to live up to the standards of the role he is to play in the spiritual development of Klal Yisrael. Yichus is not a license, it is a privilege which one must continually earn.