Even if his father or mother or brother or sister should die, he is not to defile himself, because the symbol of consecration to his God is upon his head.
After the law for the discovery and shame of those that by sin had made themselves vile, fitly follows this for the direction and encouragement of those who by their eminent piety and devotion had made themselves honourable, and distinguished themselves from their neighbours.
Commenting on Numbers 6:1-21
He shall not make himself unclean for his father or for his mother, for his brother or for his sister, when they die,.... Aben Ezra adds also, for his wife, and for his daughter, and for others; what even the priests of the Lord, the common priests might do, a Nazarite might not, not come near any of his relations when dead, as to touch...
He shall not make himself unclean for his father, or for his mother, for his brother, or for his sister, when they die: because the consecration of his God [is] upon his head. (c) In that he allowed his hair to grow, he signified that he was consecrated to God.