Jamieson, Fausset and Brown on Genesis 6:13

13. And God said unto Noah--How startling must have been the announcement of the threatened destruction! There was no outward indication of it. The course of nature and experience seemed against the probability of its occurrence. The public opinion of mankind would ridicule it. The whole world would be ranged against him. Yet, persuaded the communication was from God, through faith (He 11:7), he set about preparing the means for preserving himself and family from the impending calamity.