The writer advised his listeners to contend for the faith which was once delivered to them because their faith could be lost as it happened to the Israelites. The faith refers to that body of doctrine that was given by God through the Apostles to the church.
He said although all the Israelites were saved from Egypt yet those who did not continue to believe got destroyed. So it was with the angels who did not keep their proper place who now have been reserved in everlasting chains.
Charles Spurgeon once said that “the new views are not the old truth in a better dress, but deadly errors with which we can have no fellowship.” False doctrine is a deadly poison that must be identified, labeled, and avoided. Spurgeon also said, “I cannot endure false doctrine, however neatly it may be put before me. Would you have me eat poisoned meat because the dish in which it is served is of the choicest ware?”
Therefore, our salvation becomes only secured as we keep contending for the faith and trusting His word. If this was necessary in the era of Jude, then it becomes more necessary in our days with lots of false teachers and prophets around. Hence those who preach and teach that once saved is forever saved cannot be entirely true!
If God did not even spare the chosen Israelites who disobeyed and the angels who did not keep their proper place are now forever chained, then we cannot be an exemption if we continue to live in disbelieve and disobedient.