Dear Biju V. Joseph,
To understand the expression in Jude 3, we should consider the epistle as a whole. However, let me quote the verse under consideration. “Beloved, using all diligence to write to you of our common salvation, I have been obliged to write to you exhorting you to contend earnestly for the faith once delivered to the saints.” It starts with the word “Beloved.” They are those who have the faith that was delivered to the saints. Therefore, we could say that they are part of the saints, at any time in the history of those who are addressed in verses 1 and 2.
However, those who read this letter should be aware of the fact that there are certain men that are among them and the saints did not notice their entry (Jude 4). They pretend to be saints but not saints as called by God (Jude 1-2).
Jude go back in time and show that such entrance by unsaved people among those who were saved by God could be seen when the children of Israel were saved from Egypt. He also mentions about the evil and rebellious angels among the true angels. He also mentions about Michael in contrast to the devil. He mentions about those who went after the way of Cain and still try to be in the leadership among the saints. He also mentions about those who go in the way of Core among the saints. He also brings Enoch from the Old Testament who prophesied about the coming judgment. With these examples, Jude is telling us about the responsibility of a believer to watch out for those who try to come among us unnoticed.
We have references to such people who want to be with believers and act as one of them in Romans 5:20; Galatians 2:4; and 2 Peter 2:1. They try to be among us by pretending to be one of us, while they are not. They will deny the deity of Christ indirectly, at first. This they do by changing certain words and expression in the Word of God, or by contradicting the teachings of Christ by citing verses as Satan did when he tempted the Lord.
In this letter, Jude was asking the saints to contend for the faith once delivered to them. What is that faith? It is what we read about in the Bible. From Hebrew 11, we learn that the faith is the substantiating of things hoped for and the conviction of things not seen. We also read about a few men from the Old Testament who had faith in God and what He promised them.
What God promised us is stated succinctly in John 1:12-13, “But as many as received Him, to them gave He the right to be children of God, to those that believe on His name; Who have been born, not of blood nor of the flesh’s will nor of man’s will, but of God.” We read in Ephesians 2:4-10 that the faith that we have is a gift from God. That faith is what we read in Jude 3. We have the responsibility to contend for it, because God gave that to us as a gift.
This contending for our faith is using the Word of God as it is delivered to us. It should be as those who have entered among us unnoticed suggest. God has given to us what we need to maintain this faith in the Bible and that is the whole of it. That is what we read in 2 Timothy 3:16, “Every Scripture is divinely inspired and profitable for teaching, for conviction, for correction, for instruction in righteousness; that the man of God may be complete, fully fitted to every good works.”
I hope that his will be helpful to you. If you need additional help, please let me know. I assume that you are a believer in Christ as your personal Savior, Lord, and God.