The purpose of the epistle has been to warn and now Jude reminds them that they have been warned before. We may receive all the teaching that we need to help us to cope with the difficulties that we face in the world or in the church and yet we can forget what we hear. But why do we not treasure up such valuable instruction? We underestimate its usefulness and blithely go on to face the trials of this life on our own. But this is the word of God, who knows our trials before they come and prepares us for them beforehand. He does not teach us for nothing.