John Gill Commentary Jude 1:15

"to execute judgment upon all, and to convict all the ungodly of all their works of ungodliness which they have ungodly wrought, and of all the hard things which ungodly sinners have spoken against him." — Jude 1:15 (ASV)

To execute judgment upon all
Quick and dead, small and great, high and low, rich and poor, good and bad, righteous and wicked, sheep and goats; to pass the definitive sentence on each, that of absolution, life, and happiness, on his own people, and that of condemnation, death, and misery, on the wicked; which will be done in the most strict and righteous manner:

and to convince all that are ungodly among them
those who are without God, the fear of him love to him, or faith in him; who have lived without the worship of him, or in a false worship; and particularly false teachers are here meant, the same as in (Jude 1:4) ; who will then be convicted in their own consciences, by that clear evidence, and full light, in which things will be set:

of all their ungodly deeds
both against law and Gospel:

which they have ungodly committed
which they lived in the commission of, and continually practised in a vile manner, publicly, and in defiance of heaven, and with seared consciences:

and of all their hard [speeches], which ungodly sinners have spoken
against him
either "against" God, as the Vulgate Latin version reads, against his being, his perfections, his providence, his purposes, his word, and worship; or rather against Jesus Christ the Lord, who will come to judge them, against his person and offices, his blood, righteousness, and sacrifice; his ministers and people, his truths and ordinances.