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 5:1GENEALOGY OF THE PATRIARCHS. (Gen. 5:1-32)
book of the generations--(See Gen 11:4).
Adam--used here either as the name of the first man, or of the human race generally.
gen 5:5all the days . . . Adam lived--The most striking feature in this catalogue is the longevity of Adam and his immediate descendants. Ten are enumerated (Gen. 5:5-32) in direct succession whose lives far exceed the ordinary limits with which we are familiar--the shortest being three hundred sixty-five, [Gen 5:23] and the longest nine hundred sixty-nine years [Gen 5:27]. It is useless to inquire whether and what secondary causes may have contributed to this protracted longevity--vigorous constitutions, the nature of their diet, the temperature and salubrity of the climate; or, finally--as this list comprises only the true worshippers of God--whether their great age might be owing to the better government of their passions and the quiet, even tenor of their lives. Since we cannot obtain satisfactory evidence on these points, it is wise to resolve the fact into the sovereign will of God. We can, however, trace some of the important uses to which, in the early economy of Providence, it was subservient. It was the chief means of reserving a knowledge of God, of the great truths of religion, as well as the influence of genuine piety. So that, as their knowledge was obtained by tradition, they would be in a condition to preserve it in the greatest purity.
gen 5:21Enoch . . . begat Methuselah--This name signifies, "He dieth, and the sending forth," so that Enoch gave it as prophetical of the flood. It is computed that Methuselah died in the year of that catastrophe.
gen 5:24And Enoch walked with God--a common phrase in Eastern countries denoting constant and familiar intercourse.
was not; for God took him--In Heb 11:5, we are informed that he was translated to heaven--a mighty miracle, designed to effect what ordinary means of instruction had failed to accomplish, gave a palpable proof to an age of almost universal unbelief that the doctrines which he had taught (Jde 1:14-15) were true and that his devotedness to the cause of God and righteousness in the midst of opposition was highly pleasing to the mind of God.
gen 5:26Lamech--a different person from the one mentioned in the preceding chapter [Gen 4:18]. Like his namesake, however, he also spoke in numbers on occasion of the birth of Noah--that is, "rest" or "comfort" [Gen 5:29, Margin]. "The allusion is, undoubtedly, to the penal consequences of the fall in earthly toils and sufferings, and to the hope of a Deliverer, excited by the promise made to Eve. That this expectation was founded on a divine communication we infer from the importance attached to it and the confidence of its expression" [PETER SMITH].
gen 5:32Noah was five hundred years old: and . . . begat--That he and the other patriarchs were advanced in life before children were born to them is a difficulty accounted for probably from the circumstance that Moses does not here record their first-born sons, but only the succession from Adam through Seth to Abraham.