Two Permanent Institutions (Exodus 29:27-30).
A brief break in the narrative is now taken to emphasise the future effect of all this before we go into the personal part Aaron and his sons now take in the ceremony. Two permanent things that will affect the future for the priesthood have been instituted. 1). The wave/heave offering has been sanctified, and 2). the garments of ‘The Priest' have been sanctified. The effect on future generations is now described. The explanation of the sanctifying of the wave offering is clearly intended to follow immediately on its institution (Exodus 29:26), and it was important to deal with the future of the priestly garments here to save confusing it with what is said in Exodus 29:35-37.
“And you shall sanctify the breast of the wave offering, and the thigh (or ‘shoulder') of the heave offering, which is waved and which is heaved up, of the ram of consecration, even of that which is for Aaron and of that which is for his sons, and it shall be for Aaron and his sons as a due for ever from the children of Israel. For it is a heave offering. And it shall be a heave offering from the children of Israel of the sacrifices of their peace offerings, even their heave offering to Yahweh.”
The act of Moses in taking the breast as a wave offering is an act that ‘sanctifies' (makes holy) all future breasts and thighs/shoulders of peace offerings for consecration. In future from such peace offerings the breast will be waved before Yahweh (a few movements to and fro) and the shoulder will be ‘heaved', (that is, waved once, or possibly simply ‘contributed'), and then both will be for the priests to eat. This will be their due from the children of Israel.
“ For it is a heave offering.” This is the technical name for such offerings. It may rather mean ‘a contribution offering'. And in future the breast and thigh/shoulder will always be seen as for a heave/contribution offering from the children of Israel from all their sacrifices of peace offerings. They will by this be their heave/contribution offering to Yahweh.
The idea behind the wave offering and the heave/contribution offering is that what is waved/heaved/contributed is being offered to Yahweh but then retained for the use of His priests. It was a practical means by which priests could be provisioned, while there was at the same time no limitation on the offering of the total sacrifice to Yahweh, for it was offered by waving/heaving.
“And the holy garments of Aaron shall be for his sons after him, to be anointed in them, and to be consecrated in them. Seven days shall the son who is priest in his stead put them on when he comes into the Tent of Meeting to minister in the Holy Place.”
The second institution demonstrates what has been said earlier. The holy garments of Aaron differentiate the one known as ‘The Priest' as against the many ‘priests'. Whoever is selected to replace ‘The Priest' when he dies will have the holy garments of Aaron put on him, so as to be anointed in them and consecrated in them. And then for seven days will wear those garments in the Tent of Meeting without leaving it, as an act of dedication and consecration (see Leviticus 8:33). The consecration is to last for seven days. See for an application of this Numbers 20:28.