Adam Clarke's Commentary on the Bible

Verse 4 (Hebrews 13:4)

Marriage is honorable in all - Let this state be highly esteemed as one of God's own instituting, and as highly calculated to produce the best interests of mankind. This may have been said against the opinions of the Essenes, called Therapeutae, who held marriage in little repute, and totally abstained from it themselves as a state of comparative imperfection. At the same time it shows the absurdity of the popish tenet, that marriage in the clergy is both dishonorable and sinful; which is, in fact, in opposition to the apostle, who says marriage is honorable in All; and to the institution of God, which evidently designed that every male and female should be united in this holy bond; and to nature, which in every part of the habitable world has produced men and women in due proportion to each other.

The bed undefiled - Every man cleaving to his own wife, and every wife cleaving to her own husband, because God will judge, i.e. punish, all fornicators and adulterers.

Instead of δε but, γαρ , for, is the reading of AD*, one other, with the Vulgate, Coptic, and one of the Itala; it more forcibly expresses the reason of the prohibition: Let the bed be undefiled, For whoremongers and adulterers God will judge.

- Adam Clarke's Commentary on the Bible