In Exodus 29, God specified the clothing of the High Priest, as well as the process of his ordination. Israel did not “appoint” a High Priest on her own, nor by her own methods. God’s High Priest could only be appointed by God and in His service, must not appear like other people.
Though the vestments of the High Priest were elaborate and ornate, God does not specify the significance of each article of clothing – or of any of the articles. Perhaps the significance of this is so that Israel might not be emboldened to give greater significance to one part over the others. Elaborate though it was, confined to the High Priest though it was, it was, still, just clothing.
Israel, of course, influenced by the paganism around her, ended up worshiping the whole garment (Judges 8:27; 17:5).
The High Priest’s garments did not signified nothing about him except that He was God’s man in God’s service.
In Exodus 25 – 30, directions were given for building the tabernacle. In Exodus 36 – 40, Moses notes that Israel followed those instructions to the letter. Here in Leviticus 8, Moses indicates that the instructions of Exodus 29 were likewise followed to the letter.