The flood is a common warning example in the New Testament (1 Peter 3:20; 2 Peter 2:5; 2 Peter 3:6–7). It refers to the judgment of God. In this case, Jesus is stating that people continued with their normal day to day activities as if nothing would change and no judgment was coming.1
38 For as in those days before the flood they were eating and drinking, marrying and giving in marriage, until the day when Noah entered the ark,