Essay zu Schemot 28:36

Foremost among the symbols on Aharon’s garments is what he bears on his brow: a band with the words “Holiness for Yhwh.” It serves as a symbol of his efforts to obtain forgiveness on behalf of the Israelite people, one of his primary functions as priest. This function extends to cover even unintentional transgressions, such as accidents in the handling of sacred cultic objects.