Jude 1:13 - Matthew Poole's English Annotations on the Holy Bible

Raging waves of the sea; not only inconstant as water, but unquiet, turbulent, restless, that cannot cease from sin. Foaming out their own shame; that wickedness whereof they should be ashamed; like the troubled sea, when it cannot rest, whose waters cast up mire and dirt, Isaiah 57:20. Wandering stars; either planets properly called, or rather meteors called running stars, inconstant in their motion, uncertain in their shining, making a little show, but presently vanishing; such was the doctrine of these, which had a show of light, but a deceitful and inconstant one. To whom is reserved the blackness of darkness for ever; the thickest darkness, viz. that of hell; they would be counted lights, but are themselves cast into utter darkness, 2 Peter 2:17. As blackness of darkness shows the horror of their punishment, so its being reserved for them shows the certainty of it.