This part of the discourse began by discussing priests who had been foreordained to preach of the coming atoning mission of the Messiah. Not only were they to preach it, however, but they received the benefits of that redeeming mission even though it had not yet occurred. Just as they were ordained based on God’s foreknowledge of their actions, they could enjoy the benefits of the Atonement based on God’s foreknowledge of Christ’s actions.
Thus, they could obey the commandments, and have their garments made white, which is the metaphor for the cleansing from sin, which is a crucial aspect of the Atonement. They continued to live according to those commandments, and, therefore, they entered into the rest of the Lord. They are presented as the model for what we should also do in order to enter into the rest of the Lord.