We are here told,

I.How long the flood was increasing - forty days, Gen 7:17. The profane world, who believed not that it would come, probably when it came flattered themselves with hopes that it would soon abate and never come to extremity; but still it increased, it prevailed. Note, 1. When God judges he will overcome. If he begin, he will make an end; his way is perfect, both in judgment and mercy. 2. The gradual approaches and advances of God's judgments, which are designed to bring sinners to repentance, are often abused to the hardening of them in their presumption.

II.To what degree they increased: they rose so high that not only the low flat countries were deluged, but to make sure work, and that none might escape, the tops of the highest mountains were overflowed - fifteen cubits, that is, seven yards and a half; so that in vain was salvation hoped for from hills or mountains, Jer 3:23. None of God's creatures are so high but his power can overtop them; and he will make them know that wherein they deal proudly he is above them. Perhaps the tops of the mountains were washed down by the strength of the waters, which helped much towards the prevailing of the waters above them; for it is said (Job 12:15), He sends out the waters, and they not only overflow, but overturn, the earth. Thus the refuge of lies was swept away, and the waters overflowed the hiding-place of those sinners (Isa 28:17), and in vain they fly to them for safety, Rev 6:16. Now the mountains departed, and the hills were removed, and nothing stood a man in stead but the covenant of peace, Isa 54:10. There is no place on earth so high as to set men out of the reach of God's judgments, Jer 49:16; Oba 1:3, Oba 1:4. God's hand will find out all his enemies, Psa 21:8. Observe how exactly they are fathomed (fifteen cubits), not by Noah's plummet, but by his knowledge who weighs the waters by measure, Job 28:25.

III.What became of Noah's ark when the waters thus increased: It was lifted up above the earth (Gen 7:17), and went upon the face of the waters, Gen 7:18. When all other buildings were demolished by the waters, and buried under them, the ark alone subsisted. Observe, 1. The waters which broke down every thing else bore up the ark. That which to unbelievers is a savour of death unto death is to the faithful a savour of life unto life. 2. The more the waters increased the higher the ark was lifted up towards heaven. Thus sanctified afflictions are spiritual promotions; and as troubles abound consolations much more abound.

The Lord shut him in - This seems to imply that God took him under his especial protection, and as he shut Him in, so he shut the Others out. God had waited one hundred and twenty years upon that generation; they did not repent; they filled up the measure of their iniquities, and then wrath came upon them to the uttermost.

Fifteen cubits upwards did the waters prevail,.... Either to such an height above the earth, upwards from that, or from the high hills; for though the words do not necessarily imply that, yet it may be allowed, since there was water enough to cover the highest of them; and fifteen cubits of water were enough to drown the tallest man, or largest beast that should be upon the top of any of them:

and the mountains were covered, with water, even it may be allowed fifteen cubits high; nor will this furnish out so considerable an objection to the history of the flood as may be thought at first sight, since the highest mountains are not near so high as they are by some calculated. Sir Walter Raleigh allows thirty miles for the height of the mountains, yet the highest in the world will not be found to be above six direct miles in height. Olympus, whose height is so extolled by the poets, does not exceed a mile and a half perpendicular, and about seventy paces. Mount Athos, said to cast its shade into the isle of Lemnos (according to, Pliny eighty seven miles) is not above two miles in height, nor Caucasus much more; nay, the Peak of Teneriff, reputed the highest mountain in the world, may be ascended in three days (according to the proportion of eight furlongs to a day's journey), which makes about the height of a German mile perpendicular; and the Spaniards affirm, that the Andes, those lofty mountains of Peru, in comparison of which they say the Alps are but cottages, may be ascended in four days' compass (o).

(o) See the Universal History, vol. 1. p. 218. marg. Bedford's Scripture Chronology, ch. 12. p. 152, 153.

the waters increased, and bare up the ark--It seems to have been raised so gradually as to be scarcely perceptible to its occupants.