But; beloved ... ye - in contrast to those reprobates, Jud 1:20, again.
remember - implying that his readers had been contemporaries of the apostles. For Peter uses the very same formula in reminding the contemporaries of himself and the other apostles.
spoken before - spoken already before now.
the apostles - Peter (see on 2Pe 3:2, 2Pe 3:3), and Paul before Peter (Act 20:29; 1Ti 4:1; 2Ti 3:1). Jude does not exclude himself from the number of the apostles here, for in Jud 1:18, immediately after, he says, “they told You,” not us (rather as Greek, “used to tell you” implying that Jude’s readers were contemporaries of the apostles, who used to tell them).