Jude 1:4 - Matthew Poole's English Annotations on the Holy Bible

Who were before of old ordained; Greek, forewritten, i.e. of whom it was formerly written, or foretold, viz. by Christ and his apostles; or rather, it is to be understood according to our translation, before ordained, viz. in the eternal counsel of God; God's decree being compared to a book, in which things to be done are written down. This the apostle adds to prevent any offence that might be taken at the wickedness of these seducers; and therefore lets these saints know, that though such men crept in unawares to them, yet it was not without the providence of God so ordering it. To this condemnation; or, judgment; and it may be understood, either of a reprobate sense, to which they who thus perverted the gospel were given up by God, according to his preordination; or of that damnation he decreed should follow upon their wickedness, in making shipwreck of the faith themselves, and subverting others. This seems best to agree with 2 Peter 2:3. Turning the grace of our God into lasciviousness; abusing the doctrine of the grace of God, and benefits of Christ revealed in the gospel, especially the doctrine of Christian liberty, to the encouraging themselves and others in the vilest lusts, 2 Peter 2:1. And denying the only Lord God: either this may be understood of the Father distinctly from Christ, expressed in the following clause, and only is put in not to exclude either of the other Persons of the Trinity from being God, but to exclude idols and false gods: or it may be understood of Christ, as well as the words following; not only because there is but one article in the Greek relating to the whole sentence, but because it seems best to agree with the parallel place, 2 Peter 2:1, which is most generally understood of Christ; and because the heresies of those times, which Jude cautions these saints against, struck especially at the Godhead of Christ, which he therefore the more expressly asserts.