“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.”
King James Version (KJV)
1:3 When I gave all diligence to write to you of the common salvation - Designed for all, and enjoyed by all believers. Here the design of the epistle is expressed; the end of which exactly answers the beginning. It was needful to exhort you to contend earnestly - Yet humbly, meekly, and lovingly; otherwise your contention will only hurt your cause, if not destroy your soul. For the faith - All the fundamental truths. Once delivered - By God, to remain unvaried for ever.
Jude 1:3 When I gave all diligence to write unto you. His thought was that when he proposed to write diligently and carefully some need impelled him to write at once, more briefly perhaps than he had purposed. Earnestly contend for the faith which was once delivered unto the saints. He exhorts to contend for the faith delivered once for all, the faith without innovation, the gospel of the apostles in distinction from the adulterations of false teachers. The doctrine of a progressive revelation after the apostles is not found in the New Testament.