had spoken - Render spake. The formal appointment is only now made, in reward for their zeal Exodus 32:26-29, though reference to their future office appears previously in Leviticus 25:32 ff, and they had already acted as assistants to the priests (compare Exodus 38:21).

For the Lord had spoken unto Moses,.... Not to number the Levites, when he gave him the orders to number the rest of the tribes: this is observed, lest it should be thought that this was what Moses did of himself, out of affection to the tribe he was of, and to spare it, that it might not be obliged to go forth to war when others did; not that they were forbid to engage in war, or that it was unlawful for them so to do, for when necessity required, and they were of themselves willing to engage in it, they might, as appears in the case of the Maccabees, but they might not be forced into it; they were, as Josephus (e) says, exempted from it; and so all concerned in religious service, both among Heathens and Christians, have always been excused bearing arms:
saying; as follows.
(e) Antiqu. l. 3. c. 12. sect. 4.

Moses was not to muster the tribe of Levi along with the children of Israel, i.e., with the other tribes, or take their number, but to appoint the Levites for the service of the dwelling of the testimony (Exodus 38:21), i.e., of the tabernacle, that they might encamp around it, might take it down when the camp was broken up, and set it up when Israel encamped again, and that no stranger (zar, non-Levite, as in Leviticus 22:10) might come near it and be put to death (see Numbers 3:10). The rest of the tribes were to encamp every man in his place of encampment, and by his banner (see at Numbers 2:2), in their hosts (see Numbers 2), that wrath might not come upon the congregation, viz., through the approach of a stranger. קצף, the wrath of Jehovah, breaking in judgment upon the unholy who approached His sanctuary in opposition to His command (Numbers 8:19; Numbers 18:5, Numbers 18:22). On the expression "keep the charge" (shamar mishmereth), see at Genesis 26:5 and Leviticus 8:35.