And Cainan lived seventy years and begat Mahalaleel:

Wesley's Notes

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.

King James Translators' Notes

Mahalaleel: Gr. Maleleel

Matthew Henry's Concise Commentary

5:6-20 Concerning each of these, except Enoch, it is said, and he died. It is well to observe the deaths of others. They all lived very long; not one of them died till he had seen almost eight hundred years, and some of them lived much longer; a great while for an immortal soul to be prisoned in a house of clay. The present life surely was not to them such a burden as it commonly is now, else they would have been weary of it. Nor was the future life so clearly revealed then, as it now under the gospel, else they would have been urgent to remove to it. All the patriarchs that lived before the flood, except Noah, were born before Adam died. From him they might receive a full account of the creation, the fall, the promise, and the Divine precepts about religious worship and a religious life. Thus God kept up in his church the knowledge of his will.