They knew not - That is, they knew not the exact time until it came upon them. So, says he, it shall be when the Son of man shall come. They shall not know “the precise time” until he comes, and then they will be found engaged in the ordinary business of life unconcerned.
Related Commentaries of Matthew 24:39
Matthew 24:39
39 And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be.