Exodus 28 - God wanted clothing for the priests that would set them apart for the special ministry they had but would also cause the priest to be humble and grateful for the role they had to serve God and His people. The ephod they wore would have the names of the twelves tribes of Israel engraved on it. This would be a constant reminder to the priests that they represented God's people to their God. Bells were to be sown into the hem of their garments so they would make a sound as they moved about the tabernacle. The people would hear them and the priests would be aware of God's "ears" also hearing the sound.
Exodus 29 - This chapter deals with the offerings made before the Lord as Aaron and his sons were ordained to the work for which they were called. It should be noted that God had already ordained them to their work. The ceremony was to show that ordination to the people. This is true today as ministers know that God has already called and ordained them to serve Him before an actual "ordination service" is held. The church doesn't ordain a man. The role of the church is to publicly declare that they see God's ordination upon His servant.