17 the apostles. Here Jude assumes that he himself is not one of the apostles of Christ, but he refers to their teachings as of divine authority.

18 mockers in the last time. This is almost a verbatim quotation from II Peter 3:3. Jude quotes this as he would the Scriptures, indicating that very soon after Peter wrote his last epistle (the canonicity of which has long been rejected by false teachers, even more emphatically than most other books of the New Testament), it was known and accepted by the early church as of divine authority. This verse, incidentally, confirms that Jude understood that his epistle in all its urgency would be especially relevant to “the last time.”

19 separate themselves. This “separation” apparently refers to the proliferation of sectarian divisions and cultic offshoots from the true church in the last days. These have indeed multiplied explosively in the past two generations especially. There are now literally thousands of Christian and quasi-Christian denominations, sects, cults, and movements in the world, the vast majority of which have been formed for other than Biblical reasons.

19 sensual. “Sensual” means “self-centered.” Even in evangelical circles today, there is an altogether anti-Biblical promotion of “self-image, “self-esteem,” and “self-love” as supposed panaceas. But such counselors “have not the Spirit” of God, for He exalts Christ, not self.