Charles Spurgeon Commentary Hebrews 13:4

"[Let] marriage [be] had in honor among all, and [let] the bed [be] undefiled: for fornicators and adulterers God will judge." — Hebrews 13:4 (ASV)

Marriage is honourable in all, and the bed undefiled: but whoremongers and adulterers God will judge.

And terrible will be their doom when God does judge them.

They may think that, because they sin in secret, therefore they will escape punishment; but it will not be so. Whether men judge them or not, God will judge them.