The older daughter gave birth to a son and named him Moab. He is the father of the Moabites of today.
37. And the firstborn bare . This was a terrible blindness, that the daughters of Lot, shaking off all feeling of shame, raised up a memorial of their virtue, and through an eternal sign have exhibited their dishonor before their posterity. To their sons, or better, two nation in their persons, they give names, whence everybody can know that it was a family, originating from adultery and unchaste intercourse.
Here is, I. The great trouble and distress that Lot was brought into after his deliverance, Gen 19:30. 1. He was frightened out of Zoar, durst not dwell there; probably because he was conscious to himself that it was a refuge of his own choosing and that herein he had foolishly prescribed to God, and therefore he could not but distrust his safety in it...
Commenting on Genesis 19:30-38
And the firstborn bare a son, and called his name Moab: the same [is] the father of the Moabites unto this day. (s) Who as they were born in most horrible incest, so were they and their posterity vile and wicked.