John Calvin Commentary Numbers 6:9

"And if any man die very suddenly beside him, and he defile the head of his separation; then he shall shave his head in the day of his cleansing, on the seventh day shall he shave it." — Numbers 6:9 (ASV)

And if any man die very suddenly. Here is prescribed what must be done if a defilement should have been contracted which no precaution could have prevented. If a Nazarite should have willingly and knowingly entered a house of mourning, or should have come near a dead body, his consecration would have been violated not without sin; but, in the case of a sudden death, the error was excusable, though God commands that it should be expiated.

For whatever time of the vow had passed He counts for nothing, nor will it be taken into account. This was no light punishment, that he, who had been guilty of no fault, should begin to pay his vow altogether afresh. Besides the loss of the time, a sacrifice is also added, by which he who was polluted should prepare himself for a new consecration.

But, because this consecration was voluntary, no one could complain of the immoderate rigor to which he had subjected himself of his own accord. Meanwhile, it was shown how precious to God is the purity of His worship.³³⁷

Two Hebrew words from different roots, though they are of similar meaning, are used, by which mode of speaking Moses wished more fully to express the unexpected nature of the death. For, in my opinion, it is puerile of the Jews to understand the first of a bloody murder, the other of a sudden death.

³³⁷ פתע פתאם Each means suddenly. A. V., very suddenly. It is a rule of Hebrew Grammar that the use of two synonymous words is to be considered as a mode of expressing a superlative. — W.