Adam Clarke on 1 Thessalonians 4:5

Not in the lust of concupiscence - Having no rational object, aim, nor end. Some say, "not like beasts;" but this does not apply as they who use it wish, for the males and females of the brute creation are regular and consistent in their intercourse, and scarcely ever exceed such bounds as reason itself would prescribe to those most capable of observing and obeying its dictates.

The Gentiles which know not God - These are the beasts; their own brutes are rational creatures when compared with them. Enough has been said on this subject on Romans 1, and 2: They who wish to see more may consult Juvenal, and particularly his 6th and 9th Satires; and indeed all the writers on Greek and Roman morals.