And the Lord spake unto Moses and unto Aaron This census had a different object from the former one, which we have just been considering, viz., that an equal distribution of the charges should be made in proportion to the number of the individuals. First, as regarded age, a distinction must be observed between this tribe and the others; for we have already seen that all the Israelites above twenty years of age were numbered, because they were then fit to bear arms. But it was not without reason that a more mature age was required in the case of the Levites, so that they should not begin to discharge their ministry before their thirtieth year. For not only is strength and rigor of body requisite for spiritual warfare, but seriousness and gravity also. If they had been admitted in their youth, their levity might have detracted from the reverence due to sacred things, since the young are often led to act intemperately by their fervor and licentiousness. Access to the sanctuary, therefore, was not permitted them till they had grown up to be men; for by their thirtieth year men ought to have become so staid, as that it shall be base and inexcusable for them to give way to the wantonness of youth. From their fiftieth year they were released from their duties; since sloth and inactivity generally accompany old age. The case is different as to war, because we find many who are vigorous after their fiftieth year. Furthermore, since religion is more precious than all earthly affairs, diligent care was to be taken lest it should fall into disesteem on account of the idleness and somnolency of its ministers.

And the Lord spake unto Moses, and unto Aaron,.... After they had taken the number of the Levites, and made an exchange of the firstborn of Israel for them; and now they are ordered to number them a second time, and take out from them such as were fit for service:
saying; as follows.

The middle-aged men of the tribe of Levi, all from thirty years old to fifty, were to be employed in the service of the tabernacle. The service of God requires the best of our strength, and the prime portion of our time, which cannot be better spent than to the honour of Him who is the First and Best. And the service of God should be done when we are most lively and active. Those do not consider this who put off repentance to old age, and so leave the best work to be done in the worst time.

Rules of Service, and Numbering of the Levites Qualified for Service. - After the adoption of the Levites for service at the sanctuary, in the place of the first-born of Israel, Moses and Aaron mustered the three families of the Levites by the command of God for the service to be performed by those who were between the ages of 30 and 50. The particulars of the service are first of all described in detail (vv. 4-33); and then the men in each family are taken, of the specified age for service (vv. 34-49). The three families are not arranged according to the relative ages of their founders, but according to the importance or sacredness of their service. The Kohathites take the lead, because the holiest parts of the tabernacle were to be carried and kept by this family, which included the priests, Aaron and his sons. The service to be performed by each of the three Levitical families is introduced in every case by a command from God to take the sum of the men from 30 years old to 50 (see Numbers 4:1-3, Numbers 4:21-23, Numbers 4:29 and Numbers 4:30).