“For as in those days which were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noah entered into the ark, and they did not know until the flood came, and took them all away, so will be the coming of the Son of man.”
So sudden and unexpected would be the final event that most would be caught unawares when the end came. The similarity lies in the fact that in the days before the Flood men ate and drank, and married and gave in marriage, in the same way as they did in Jesus' day. In other words they lived what seemed like normal everyday lives. But both ignored the preaching of a Preacher of Righteousness (see 2 Peter 2:5). The result was that the flood came upon them unexpectedly, and carried them away, in the same way as the coming of the Son of Man will one day do the same with the same unexpectedness.