2-peter 3:6

Whereby - Δι ̓ ὧν Di' hōn. Through which, or by means of which. The pronoun here is in the plural number, and there has been much difference of opinion as to what it refers. Some suppose that it refers to the heavens mentioned in the preceding verse, and to the fact that the windows of heaven were opened in the deluge (Doddridge), others that the Greek phrase is taken in the sense of (διὸ dio) "whence." Wetstein supposes that it refers to the "heavens and the earth." But the most obvious reference, though the plural number is used, and the word "water" in the antecedent is in the singular, is to "water." The fact seems to be that the apostle had the "waters" mentioned in Genesis prominently in his eye, and meant to describe the effect produced "by" those waters. He has also twice, in the same sentence, referred to "water" - "out of the water and in the water." It is evidently to these "waters" mentioned in Genesis, out of which the world was originally made, that he refers here. The world was formed from that fluid mass; by these waters which existed when the earth was made, and out of which it arose, it was destroyed. The antecedent to the word in the plural number is rather that which was in the mind of the writer, or that of which he was thinking, than the word which he had used.

The world that then was ... - Including all its inhabitants. Rosenmuller supposes that the reference here is to some universal catastrophe which occurred before the deluge in the time of Noah, and indeed before the earth was fitted up in its present form, as described by Moses in Genesis 1. It is rendered more than probable, by the researches of geologists in modern times, that such changes have occurred; but there is no evidence that Pater was acquainted with them, and his purpose did not require that he should refer to them. All that his argument demanded was the fact that the world had been once destroyed, and that therefore there was no improbability in believing that it would be again. They who maintained that the prediction that the earth would be destroyed was improbable, affirmed that there were no signs of such an event; that the laws of nature were stable and uniform; and that as those laws had been so long and so uniformly unbroken, it was absurd to believe that such an event could occur. To meet this, all that was necessary was to show that, in a case where the same objections substantially might be urged, it had actually occurred that the world had been destroyed. There was, in itself considered, as much improbability in believing that the world could be destroyed by water as that it would be destroyed by fire, and consequently the objection had no real force. Notwithstanding the apparent stability of the laws of nature, the world had been once destroyed; and there is, therefore, no improbability that it may be again. On the objections which might have been plausibly urged against the flood, see the notes at Hebrews 11:7.

3:6 Through which - Heaven and earth, the windows of heaven being opened, and the fountains of the great deep broken up.The world that then was - The whole antediluvian race. Being overflowed with water, perished - And the heavens and earth themselves, though they did not perish, yet underwent a great change. So little ground have these scoffers for saying that all things continue as they were from the creation.