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.

And the waters prevailed exceedingly on the earth,.... Yet more and more, so that the people without the ark were obliged to remove, not only from the lower to the higher rooms in their houses, and to the tops of them, but to the highest trees; and when these were bore down, to the highest hills and mountains; and to those it was in vain to fly, by what follows:

and all the high hills that were under the whole heaven were covered: whence it appears there were hills before the flood, and that these were not caused by it, and that the deluge was universal, since there was not a hill under the whole heaven but what was covered with it. In Deucalion's flood all men are said to perish, except a few who fled to the high mountains (n); which story seems to be hammered out of this account.

(n) Apollodorus, de Deor. Origin. l. 1. p. 19.

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