The actual lighting of the lamps (compare the marginal references) was to be done to set forth symbolically the special presence which God had now Numbers 7:89 actually established among His people.

And the Lord spake unto Moses,.... Whether immediately after the offerings of the princes, or at another time, is not certain; Aben Ezra thinks it was in the night God spake unto him, because then the lamps were lighted and burning:
saying; as follows.

Aaron himself lighted the lamps, thus representing his Divine Master. The Scripture is a light shining in a dark place, 2-Peter 1:19. A dark place even the church would be without it; as the tabernacle, which had no window, would have been without the lamps. The work of ministers is to light these lamps, by expounding and applying the word of God. Jesus Christ is the only Light of our dark, sinful world; and by his atonement, by his word and the Holy Spirit, he diffuses light around.

HOW THE LAMPS ARE TO BE LIGHTED. (Numbers 8:1-4)
the Lord spake unto Moses--The order of this chapter suggests the idea that the following instructions were given to Moses while he was within the tabernacle of the congregation, after the princes had completed their offering. But from the tenor of the instructions, it is more likely that they were given immediately after the Levites had been given to the priests (see on Numbers. 3:1-4:49), and that the record of these instructions had been postponed till the narrative of other transactions in the camp had been made [PATRICK].

Consecration of the Levites. - The command of God to consecrate the Levites for their service, is introduced in Numbers 8:1-4 by directions issued to Aaron with regard to the lighting of the candlestick in the dwelling of the tabernacle. Aaron was to place the seven lamps upon the candlestick in such a manner that they would shine פּניו אל־מוּל. These directions are not a mere repetition, but also a more precise definition, of the general instructions given in Exodus 25:37, when the candlestick was made, to place the seven lamps upon the candlestick in such a manner that each should give light over against its front, i.e., should throw its light upon the side opposite to the front of the candlestick. In itself, therefore, there is nothing at all striking in the renewal and explanation of those directions, which committed the task of lighting the lamps to Aaron; for this had not been done before, as Exodus 27:21 merely assigns the daily preparation of the candlestick to Aaron and his sons; and their being placed in the connection in which we find them may be explained from the signification of the seven lamps in relation to the dwelling of God, viz., as indicating that Israel was thereby to be represented perpetually before the Lord as a people causing its light to shine in the darkness of this world. And when Aaron is commanded to attend to the lighting of the candlestick, so that it may light up the dwelling, in these special instructions the entire fulfilment of his service in the dwelling is enforced upon him as a duty. In this respect the instructions themselves, coupled with the statement of the fact that Aaron had fulfilled them, stand quite appropriately between the account of what the tribe-princes had done for the consecration of the altar service as representatives of the congregation, and the account of the solemn inauguration of the Levites in their service in the sanctuary. The repetition on this occasion (Exodus 27:4) of an allusion to the artistic character of the candlestick, which had been made according to the pattern seen by Moses in the mount (Exodus 25:31.), is quite in keeping with the antiquated style of narrative adopted in these books.