Jamieson, Fausset and Brown on Genesis 7:24

24. an hundred and fifty days--a period of five months. Though long before that every living creature must have been drowned, such a lengthened continuance of the flood was designed to manifest God's stern displeasure at sin and sinners. Think of Noah during such a crisis. We learn (Eze 14:14) that he was a man who lived and breathed habitually in an atmosphere of devotion; and having in the exercise of this high-toned faith made God his refuge, he did not fear "though the waters roared and were troubled; though the mountains shook with the swelling thereof" [Psa 46:3].