Jude 3 Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you, and exhort you that ye should earnestly contend for the faith which was once delivered unto the saints.
This verse is often misapplied. Some say that the 'faith' once delivered is the reformed teachings they adhere to. And because they believe this they reject the doctrinal information the Lord has graciously opened up to His people at this time of the end. "Can't be," they say, when hearing about the end of the Church Age, or that Christ made payment for sins at the foundation of the world, "that's not part of the faith which was once delivered to the saints."
However, in saying this they have missed the truth of God's Word once again. "The faith" once delivered to (unto) the saints is not referring to their understanding of what reformed doctrine is; no, it’s actually referring to the Lord Jesus Christ who is Himself the essence of faith.
First, if you ask the people who use this verse exactly when was the faith once delivered to the saints? And I do mean exactly when? They are not able to answer this because if they are referring to the Bible—the Bible has been handed down from generation to generation to the people of God. It was written over the span of about 1,500 years. There's no way anyone could pinpoint in an exclusive way one particular time in which the Bible was delivered to the saints.
Or, if they say it is reformed doctrine, or any other kind of doctrine, again, ask them, "exactly when was it that doctrine was summarized and completed and handed to the saints at one time?" There will be no proper answer given to this because the fact is that doctrine has developed over the course of the Church Age. One of the purposes for the reformation of a few hundred years ago was so that doctrine could be corrected to some degree and made known to the saints.
No, "the faith" once delivered is not the Bible itself. And it is not the doctrine that the church has established. It cannot be either of those things.
But we know that God says He is love (1 John 4:16). And we also know that the Bible tells us that Jesus is the Truth (John 14:6) wisdom and righteousness (1 Corinthians 1:30) as well as being the essence of faith (called Faithful and True):
Revelation 19:11 And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True,
Jesus is the Faith once delivered unto the saints (God's elect). Once delivered in order to make payment for sins at the foundation of the world (Revelation 13:8) and once delivered to the Roman authorities to demonstrate that glorious truth in 33 AD:
Matthew 27:2 And when they had bound him, they led him away, and delivered him to Pontius Pilate the governor.
18 For he knew that for envy they had delivered him.
26 Then released he Barabbas unto them: and when he had scourged Jesus, he delivered him to be crucified.
Mark 9:31 For he taught his disciples, and said unto them, The Son of man is delivered into the hands of men, and they shall kill him; and after that he is killed, he shall rise the third day.
Luke 24:7 Saying, The Son of man must be delivered into the hands of sinful men, and be crucified, and the third day rise again.
20 And how the chief priests and our rulers delivered him to be condemned to death, and have crucified him.
John 19:11 Jesus answered, Thou couldest have no power at all against me, except it were given thee from above: therefore he that delivered me unto thee hath the greater sin.
16 Then delivered he him therefore unto them to be crucified. And they took Jesus, and led him away.
Jesus (the Faith) once delivered to the saints (for the elect of God).