These are wells without water, clouds that are carried with a tempest; to whom the mist of darkness is reserved for ever. Wells - "clouds," in Jude 1:12-13, both promising (cf. 2 Peter 2:19) water, but yielding none. So their "great swelling words" are found, on trial, to be but "vanity" (2 Peter 2:18).
Clouds. 'Aleph (') A B C read х homichlai (G3658a)] 'mists:' dark, not bright as "clouds" often are; whence the latter is applied to the saints: fit emblem of the children of darkness. "Clouds" is inserted from Jude 1:12, where it is appropriate - "clouds ... without water" (promising what they do not perform); not here.
Mist, х zofos (G2217)] - blackness: 'the chilling horror accompanying darkness' (Bengel).