John Calvin Commentary Jude 1:12

"These are they who are hidden rocks in your love-feasts when they feast with you, shepherds that without fear feed themselves; clouds without water, carried along by winds; autumn leaves without fruit, twice dead, plucked up by the roots;" — Jude 1:12 (ASV)

These are spots in your feasts of charity. Those who read, “among your charities,” do not, I think, sufficiently explain the true meaning. For he calls those feasts charities (ἀγάπαις), which the faithful held among themselves to testify to their brotherly unity. Such feasts, he says, were disgraced by impure men, who afterwards ate to excess; for in these feasts, there was the greatest frugality and moderation. It was, therefore, not right that these gorgers should be admitted, who afterwards indulged themselves to excess elsewhere.

Some copies have, “Feasting with you,” which reading, if accepted, means that they were not only a disgrace but also troublesome and expensive, as they ate greedily without restraint at the church's public expense. Peter (2 Peter 2:13) speaks somewhat differently, saying that they took delight in errors and feasted together with the faithful, as if he had said that those who cherished such noxious serpents acted inconsiderately, and that those who encouraged their excessive luxury were very foolish. And today, I wish some good men had more judgment, who, by seeking to be extremely kind to wicked men, bring great damage to the whole church.

Clouds they are without water. The two comparisons found in Peter are here combined into one, but for the same purpose, for both condemn vain ostentation: these unprincipled men, though promising much, were nevertheless barren and empty within, like clouds driven by stormy winds, which give hope of rain but soon vanish into nothing. Peter adds the comparison of a dry and empty fountain; but Jude employs other metaphors for the same purpose, that they were trees fading, just as the vigor of trees disappears in autumn. He then calls them trees unfruitful, rooted up, and twice dead, as if he had said that there was no sap within, though leaves might appear.