Moses had to consecrate (or sanctify) Aaron and his sons to serve the Lord. The focus on making the priests holy appears throughout the ceremonies (29:6, 21, 28, 29, 34, 36, 37). God set them apart not only for service. But he set them apart to serve a God whose nature is very different from that of sinful humans. Leviticus 8 gives the account of how they followed these instructions.