Chapter 28 begins with a description of the clothes to be worn by Aaron and his priestly descendants. They are to make “a breastpiece, an ephod, a robe, a woven tunic, a turban and a sash,” from “gold, and blue, purple and scarlet yarn, and fine linen” (28:4-5). It then goes on to describe how to make these items. “Whenever Aaron enters the Holy Place, he will bear the names of the sons of Israel over his heart on the breastpiece of decision as a continuing memorial before the Lord.” Of course God will not forget who the twelve tribes are but it is their way of being assured he remembers them and of their recognition that they are his people. Aaron was also to put the Urim and the Thummim in the breastpiece, so they would be over his heart whenever he entered the presence of the Lord. Thus Aaron would always carry the means of making decisions for the Israelites over his heart before the Lord. We aren’t sure what these two items were but they were used to seek the Lord’s will. Perhaps if the answer was “no” they would both land one way up and if “yes” the other and if they landed opposite ways up then God was not providing an answer. This may seem like pure chance but they understood that God would direct the Urim and Thummim.
In chapter 29, God details the sacrifices that need to be made to purify Aaron for priestly work and the atonement which must be made to make the altar holy. Every day in perpetuity the Israelites were to offer two lambs on the altar, one in the morning and one at twilight. If they obeyed these regulations God would dwell among them and be their God. If they failed to obey the implication is that he would not dwell among them.
There was also to be an incense altar where Aaron would burn incense in the morning and at twilight. This altar was not to have any other offerings touch it, but once a year it was to be atoned for with the blood of the sin offering. The purpose in all of these regulations was so that “You shall consecrate them [people and objects] so they will be most holy, and whatever touches them will be holy.” God desires a holy people committed to him and his ways. Those who do not take him seriously are to be cut off from the people (30:33, 38; Gen 17:14).