John Calvin Commentary Numbers 26:8

"And the sons of Pallu: Eliab." — Numbers 26:8 (ASV)

And the sons of Pallu; Eliab. The curtailment that had occurred in the senior line is introduced here, either in exaltation of God’s grace, because, despite so great a loss, the tribe of Reuben was still numerous; or else to mark the cause of its diminution, as it might otherwise have seemed strange that other tribes exceeded in numbers the one whose founder and parent was Jacob’s first-born.

But when he has narrated how the two sons of Eliab had been destroyed with their company, he briefly refers to God’s clemency towards the sons of Korah, in that He spared them.

Surely this was no ordinary act of mercy: not only to preserve them unharmed by the calamity but afterwards to raise up shoots from the accursed root, in whom His spiritual riches might shine forth for the general benefit of the Church. For we know what honorable mention is often made of this family; and it is probable that some of them authored certain Psalms and were thus endowed with the Spirit of prophecy, when perhaps at that time none of the priests possessed this gift.

This is that profound abyss in the various and unequal judgments of God, which it is fitting for us to adore with sober humility.

Meanwhile, Moses hints in a single word at the reason why he repeats this same history: so that the formidable manner of their death might be held up as a perpetual example. For the Hebrew word נס, nes, which is primarily a standard¹⁹³ or banner, is often used for something portentous that strikes people’s senses with astonishment and at the same time fills their minds with fear.

¹⁹³ “Un mot Hebrieu qui signifie tant banniere, que mas de navire, ou une haute perche;” a Hebrew word which signifies a banner, as well as the mast of a ship, or a high pole. — Fr..