Jude 1:5
I will therefore put you in remembrance, though ye once knew this, how that the Lord, having saved the people out of the land of Egypt, afterward destroyed them that believed not. I will therefore put you in remembrance, though ye once knew this, how that the Lord, having saved the people out of the land of Egypt, afterward destroyed them that believed not.
Jude gives a remembrance to those who once knew the truth, recalling how the Lord saved the people out of the land of Egypt and afterward destroyed those who did not believe. That remembrance is given to exhort them to earnestly contend for the faith once delivered to the saints. The Lord in the verse is Christ, the invisible Leader who delivered Israel from Egyptian bondage, gave Moses the instruction to repeat to Israel, pledged to lead more than a million people safely to the promised land as His own family if they followed His guidance, and was personally interested in every one of them.
Their destruction was brought by unbelief, rebellion, murmuring against Moses and Aaron for bringing them out of Egypt, ingratitude, self-exaltation, and failure to appreciate the wonderful work of their divine Leader to deliver them and lead them to the promised land. Obedience would have kept everyone who started from Egypt from falling in the wilderness to disease or death, and keeping in mind the evidence that Moses talked with God would have preserved them from all harm. Deliverance does not protect persistent unbelievers from destruction, so past rescue does not protect people who turn from faith and disobey God.
The verse is spoken after describing the corruptions that came into the church and as part of the call to earnestly contend for the faith once delivered to the saints, because ungodly men have crept in unawares, turning grace into lasciviousness and denying the Lord. It belongs to a passage that describes the pollution of the world and the working agencies of Satan to corrupt the world. It stands with the angels who kept not their first estate and are reserved in chains to judgment and with Sodom and Gomorrah suffering vengeance as examples of that judgment, and with Michael the Archangel contending, showing scenes in the heavenly courts where angels of highest rank take interest and active part in the affairs of men and earthly kingdoms.
The faith to be contended for is the gospel of Christ to be proclaimed with earnestness and zeal to bring men back from transgression of God's commandments, arousing commandment-breakers to prepare to meet God by raising the standard of truth and magnifying the law and making it honorable. This remembrance is that faith to be stood for in moral power before the people even while voicing the message of the third angel brings opposition as Satan brings every device to make that truth of none effect. The verse stands as a present warning about apostasy to be met in this day, when men depart from the faith and false teachers arise and become actively zealous. It is to be studied earnestly and made prominent in discourses and kept constantly before the people who live in these last days so they learn their dangers and how to avoid them.
The verse guards believers against the seductive influences of false teachers, men who have a form of godliness but who are not safe leaders. At a time when all kinds of theories are presented to divert minds from the very truth that defines the position that can be occupied with safety, when Satan is working with power upon religionists, leading them to make a pretense of being righteous but to fail of placing themselves under the guidance of the Holy Spirit, workers must contend for the faith against them. The verse presses those living in the world to come out and be separate, not participating in worldly amusements and alluring schemes nor adopting worldly policies and practices, but laboring with all God-given ability to save perishing souls.