2 Samuel 10:4 - Coke's Commentary on the Holy Bible

Wherefore Hanum took David's servants, &c.— The wearing of long beards and garments was then, as it still is, the fashion of the East, where they were deemed badges of honour; and, consequently, the cutting off or curtailing of either was regarded as the greatest indignity. Nay, in some places, the cutting off of the beard was not only looked upon as matter of the highest reproach, but also of the severest punishment. So it was anciently among the Indians, and is at this day among the Persians. It was one of the most infamous punishments of cowardice in Sparta, that they who turned their backs in the day of battle were obliged to appear abroad with one half of their beard shaved, and the other half unshaved. There were two reasons which caused the Easterns of old, as well as at present, to look upon the beard as venerable: in the first place, they considered it as a natural ornament designed to distinguish men from women; secondly, it was the mark of a free man in opposition to slaves: so that, in every view, the insult of Hanun to the ambassadors of David was capital. It was a violation of the laws of hospitality, and of the right of nations. See Tavernier's Voyages to the Indies, part 2: book 2 chap. 7.