John Calvin Commentary Deuteronomy 32:41

"If I whet my glittering sword, And my hand take hold on judgment; I will render vengeance to mine adversaries, And will recompense them that hate me." — Deuteronomy 32:41 (ASV)

If I whet my glittering sword. The conditional particle does not leave the matter doubtful or in suspense but should be understood as an adverb of time. It is as if He said that as soon as He takes up arms, the destruction of His enemies will be certain. This is not to say that God needs weapons for the overthrow of His enemies. Similarly, when He adds immediately afterwards, When my hand shall have taken hold of judgment, He does not mean that judgment is ever taken from Him or escapes Him, but He thereby indicates its present and manifest operation.²⁹⁵

Therefore, when God spares His enemies, He seems, so to speak, to have thrown aside His weapons and to be at rest, having ceased to carry out the office of judge. He declares that His arms will be ready with which to destroy His enemies. Furthermore, He declares that He will then once more take up the judgment He had seemed to set aside. With these words, He indirectly criticizes the foolish security of those who imagine that His power is annihilated unless He openly exerts it, and that the judgment He postpones is entirely extinct.

²⁹⁵ “C’est pour signifier un effet present et manifest, lequel n’estoit point apparu devant;” it is to signify a present and manifest effect, which had appeared before. — Fr..