The Threefold Offering of the Levites As A Wave-offering to Yahweh (Numbers 8:10-15).
“ And you shall present the Levites before Yahweh. And the children of Israel shall lay their hands on the Levites, and Aaron shall offer the Levites before Yahweh for a waveoffering, on the behalf of the children of Israel, that it may be theirs to do the service of Yahweh.”
It is repeated that the Levites were to be presented, but this time more directly as ‘before Yahweh' (being ‘presented before the Tent of meeting' usually means precisely this). Then representatives of the people would come forward, probably the princes, and on behalf of all the people lay their hands on the Levites, identifying the people with them. The Levites were being offered to perform service on their behalf. The Levites were then officially ‘waved' (specially presented) before Yahweh by Aaron, clothed in all his High Priestly regalia, acting again on behalf of the people. The wave offering is offered or described three times, once by Aaron (verse 11), and twice by Moses (Numbers 8:13 & Numbers 8:15), emphasising its completeness. The purpose was that from then on they would ‘do the service of Yahweh'. While journeying it would be an arduous service with the constant dismantling and erecting of the Dwellingplace, packing it on the carts and taking it off, and the bearing of the furniture through the wilderness, to say nothing of the constant guard duty when the camp was at rest, together with other duties.
“ And the Levites shall lay their hands on the heads of the bullocks, and you must offer the one for a purification for sin offering, and the other for a whole burnt offering, to Yahweh, to make atonement for the Levites.”
The Levites would then identify themselves with the offerings by laying their hands on them. These offerings would result in their dedication and purification, but most of all they would make them at one with God, ‘covered' before God. They would be atoned for.
“ And you shall set the Levites before Aaron, and before his sons, and offer them for a waveoffering to Yahweh.”
Either this is a different waveoffering, an offering repeated threefold (ceremonies can be very repetitive in order to bring out different points) or verse 11 had simply mentioned this in a preparatory fashion, and this was now its fulfilment. But it may well be that there were three such presentations (Numbers 8:11; Numbers 8:13; Numbers 8:15). Such threefold presentations often occur in ceremonies. Then the purpose of this one would have been to present them on behalf of Aaron and his sons. Thus first they had been offered as an offering of the children of Israel (Numbers 8:11), here they are offered on behalf of Aaron and his sons, and in Numbers 8:15 they are offered wholly to Yahweh in order to replace the firstborn.
“ Thus shall you separate the Levites from among the children of Israel; and the Levites shall be mine.”
And this was how the Levites would be separated off from the children of Israel and become Yahweh's. From then on they would belong to Yahweh. They would be wholly set apart to His service.
“And after that shall the Levites go in to do the service of the tent of meeting.”
Once that had occurred they could perform their service for the Tent of meeting. From this point on it would be their responsibility to generally maintain and care for the accoutrements for the worship of the Sanctuary as far as it was allowed.
The Levites Wholly Given to Yahweh Instead of the Firstborn of Israel (Numbers 8:16).
Numbers 8:15-16 (15b-16)
“And you shall cleanse them, and offer them for a waveoffering, for they are wholly given to me from among the children of Israel; instead of all that opens the womb, even the first-born of all the children of Israel, have I taken them to me.”
This now gives another reason why they needed to be cleansed, and offered as a waveoffering. It was because they were being offered as substitutes for the male firstborn of the children of Israel. They were being taken instead of them (compare 3:45-51). This is a further explanation of why Moses had to offer them, and may indicate a third step in the ceremony.