John Calvin Commentary Genesis 19:35

"And they made their father drink wine that night also: and the younger arose, and lay with him; and he knew not when she lay down, nor when she arose." — Genesis 19:35 (ASV)

And the younger arose, and lay with him. This passage teaches us how dangerous it is to fall into the snares of Satan. For whoever is once caught in them becomes more deeply entangled. It is certain that Lot had been a modest man; but either the daughters took advantage of him while he was overcome with sadness, or he was lured by some other means into excessive drinking. Once having fallen into excessiveness, he was again deceived the next day.

We must therefore diligently resist the initial temptation, because those who are once stupefied by its sweetness find it nearly impossible not to lose themselves completely in vices. Therefore, people ought to be on their guard against incitements to evil, as deadly evils; and they ought to fear every flattering temptation as something poisonous. And this circumstance deserves attention: Lot, among the Sodomites, amidst an accumulation of crimes that nearly defiled heaven and earth, remained chaste and clean, like an angel.

How did he maintain such cleanness in Sodom, if not through the knowledge of the evil that surrounded him, which made him wary and careful? Now, being safe on the mountain, Satan besieges him with new pitfalls. Through this example, the Spirit admonishes us to be watchful, so that, when we least expect it, an invisible enemy lays snares for us. Likewise, Moses told earlier that Adam was deceived in Paradise. If we are vigilant for ourselves, that watchfulness will keep us on guard against all the guiles of our enemy. For everyone carries with them thousands of temptations to their own deception.