A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
gen 8:1ASSUAGING OF THE WATERS. (Gen 8:1-14)
And God remembered Noah--The divine purpose in this awful dispensation had been accomplished, and the world had undergone those changes necessary to fit it for becoming the residence of man under a new economy of Providence.
and every living thing . . . in the ark--a beautiful illustration of Mat 10:29.
and God made a wind to pass over the earth--Though the divine will could have dried up the liquid mass in an instant, the agency of a wind was employed (Psa 104:4) --probably a hot wind, which, by rapid evaporation, would again absorb one portion of the waters into the atmosphere; and by which, the other would be gradually drained off by outlets beneath.
gen 8:4seventh month--of the year--not of the flood--which lasted only five months.
rested--evidently indicating a calm and gentle motion.
upon the mountains of Ararat--or Armenia, as the word is rendered (Kg2 19:37; Isa 37:38). The mountain which tradition points to as the one on which the ark rested is now called Ara Dagh, the "finger mountain." Its summit consists of two peaks, the higher of which is 17,750 feet and the other 13,420 above the level of the sea.
gen 8:5And the waters decreased continually--The decrease of the waters was for wise reasons exceedingly slow and gradual--the period of their return being nearly twice as long as that of their rise.
gen 8:6at the end of forty days--It is easy to imagine the ardent longing Noah and his family must have felt to enjoy again the sight of land as well as breathe the fresh air; and it was perfectly consistent with faith and patience to make inquiries whether the earth was yet ready.
gen 8:7And he sent forth a raven--The smell of carrion would allure it to remain if the earth were in a habitable state. But it kept hovering about the spot, and, being a solitary bird, probably perched on the covering.
gen 8:8Also he sent forth a dove--a bird flying low and naturally disposed to return to the place of her abode.
gen 8:10again he sent forth the dove--Her flight, judging by the time she was abroad, was pursued to a great distance, and the newly plucked olive leaf, she no doubt by supernatural impulse brought in her bill, afforded a welcome proof that the declivities of the hills were clear.
gen 8:12he . . . sent forth the dove: which returned not . . . any more--In these results, we perceive a wisdom and prudence far superior to the inspiration of instinct--we discern the agency of God guiding all the movements of this bird for the instruction of Noah, and reviving the hopes of his household.
other seven days--a strong presumptive proof that Noah observed the Sabbath during his residence in the ark.
gen 8:13Noah removed the covering of the ark--probably only as much of it as would afford him a prospect of the earth around. Yet for about two months he never stirred from his appointed abode till he had received the express permission of God. We should watch the leading of Providence to direct us in every step of the journey of life.
gen 8:15DEPARTURE FROM THE ARK. (Gen 8:15-22)
And God spake . . . Go forth--They went forth in the most orderly manner--the human occupants first, then each species "after their kinds" [Gen 8:19], literally, "according to their families," implying that there had been an increase in the ark.
gen 8:20Noah builded an altar--literally, "a high place"--probably a mound of earth, on which a sacrifice was offered. There is something exceedingly beautiful and interesting to know that the first care of this devout patriarch was to return thanks for the signal instance of mercy and goodness which he and his family had experienced.
took of every clean beast . . . fowl--For so unparalleled a deliverance, a special acknowledgment was due.
gen 8:21And the Lord smelled a sweet savour--The sacrifice offered by a righteous man like Noah in faith was acceptable as the most fragrant incense.
Lord said in his heart--same as "I have sworn that the waters of Noah should no more go over the earth" (Isa 54:9).
for--that is, "though the imagination is evil"; instead of inflicting another destructive flood, I shall spare them--to enjoy the blessings of grace, through a Saviour.
gen 8:22While the earth remaineth--The consummation, as intimated in Pe2 3:7, does not frustrate a promise which held good only during the continuance of that system. There will be no flood between this and that day, when the earth therein shall be burnt up [CHALMERS].