John Lightfoot on Matthew 24:37

[But as the days of Noe were, &c.] Thus Peter placeth as parallels, the ruin of the old world, and the ruin of Jerusalem, 1 Peter 3:19-21; and by such a comparison his words will be best understood. For, see how he skips from the mention of the death of Christ to the times before the flood, in the eighteenth and nineteenth verses, passing over all the time between. Did not the Spirit of Christ preach all along in the times under the law? Why then doth he take an example only from the times before the flood? that he might fit the matter to his case, and shew that the present state of the Jews was like theirs in the times of Noah, and that their ruin should be like also. So, also, in his Second Epistle, chapter 3:6,7.

The age or generation of the flood hath no portion in the world to come: thus Peter saith, that "they were shut up in prison": and here our Saviour intimates that "they were buried in security," and so were surprised by the flood.