5:6-19 We have here all that the Holy Ghost thought fit to leave upon record concerning five of the patriarchs before the flood, Seth, Enos, Cainan, Mahalaleel, and Jared. There is nothing observable concerning any of those particularly, tho' we have reason to think they were men of eminency, both for prudence and piety: But in general, observe how largely and expressly their generations are recorded. We are told how long they lived that lived in God's fear, and when they died, that died in his favour; but as for others it is no matter: the memory of the just is blessed, but the name of the wicked shall rot. That which is especially observable, is, that they all lived very long; not one of them died 'till he had seen the revolution of almost eight hundred years, and some of them much longer; a great while for an immortal soul to be imprisoned in an house of clay. The present life surely was not to them such a burden as commonly it is now, else they would have been weary of it; nor was the future life so clearly revealed then, as it is now under the gospel, else they would have been impatient to remove it. Some natural causes may be assigned for their long life in those first ages. It is very probable that the earth was more fruitful, the products of it more strengthening, the air more healthful, and the influences of the heavenly bodies more benign before the flood than they were after. Though man was driven out of paradise, yet the earth itself was then paradisaical; a garden in comparison with its present state: and some think, that their knowledge of the creatures and their usefulness both, for their food and medicine, together with their sobriety and temperance, contributed much to it; yet we do not find that those who were intemperate, as many were, Luke 17:27, as short - lived as temperate men generally are now. It must therefore chiefly be resolved into the power and providence of God; he prolonged their lives, both for the more speedy replenishing of the earth, and for the more effectual preservation of the knowledge of God and religion, then when there was no written word, but tradition was the channel of its conveyance. All the patriarchs here (except Noah) were born before Adam died, so that from him they might receive a full account of the creation, paradise, the fall, the promise, and those divine precepts which concerned religious worship and a religious life: and if any mistake arose, they might have recourse to him while he lived, as to an oracle, for the rectifying of it, and after his death to Methuselah, and others that had conversed with him; so great was the care of Almighty God to preserve in his church the knowledge of his will, and the purity of his worship.

Genesis 5:10 Parallel Commentaries

Influences that Gave Rise to the Priestly Laws and Histories
[Sidenote: Influences in the exile that produced written ceremonial laws] The Babylonian exile gave a great opportunity and incentive to the further development of written law. While the temple stood, the ceremonial rites and customs received constant illustration, and were transmitted directly from father to son in the priestly families. Hence, there was little need of writing them down. But when most of the priests were carried captive to Babylonia, as in 597 B.C., and ten years later the temple …
Charles Foster Kent—The Origin & Permanent Value of the Old Testament

The Promise to the Patriarchs.
A great epoch is, in Genesis, ushered in with the history of the time of the Patriarchs. Luther says: "This is the third period in which Holy Scripture begins the history of the Church with a new family." In a befitting manner, the representation is opened in Gen. xii. 1-3 by an account of the first revelation of God, given to Abraham at Haran, in which the way is opened up for all that follows, and in which the dispensations of God are brought before us in a rapid survey. Abraham is to forsake …
Ernst Wilhelm Hengstenberg—Christology of the Old Testament

Appendix xii. The Baptism of Proselytes
ONLY those who have made study of it can have any idea how large, and sometimes bewildering, is the literature on the subject of Jewish Proselytes and their Baptism. Our present remarks will be confined to the Baptism of Proselytes. 1. Generally, as regards proselytes (Gerim) we have to distinguish between the Ger ha-Shaar (proselyte of the gate) and Ger Toshabh (sojourner,' settled among Israel), and again the Ger hatstsedeq (proselyte of righteousness) and Ger habberith (proselyte of the covenant). …
Alfred Edersheim—The Life and Times of Jesus the Messiah