once: a single occurrence in time, either a plain count (one occasion) or a decisive "once for all" that is never repeated
The word simply means "once," a single occurrence in time. Long before the New Testament it could point either way: to a plain count, as when Herodotus notes something happening "once a year," or to a decisive "once for all" that can never be undone. Aeschylus used it in a line that reads almost like a challenge the gospel would later answer: once a man is dead, there is no resurrection.
Which shade the word carries is decided entirely by the setting, not by any change in the word itself. When Paul says he was stoned once, or when the high priest enters the inner sanctuary once a year, it is a simple count. When Hebrews says Christ was offered once to bear the sins of many, the same word means once and never again, the single turning point of God's saving work.
In one fixed expression, "once and twice," the word does not mean a literal two times at all. The phrase is a Greek and Hebrew way of saying "again and again," and Paul uses it to thank the Philippians for sending help more than once.
A strengthened relative, ἐφάπαξ, presses the same "once for all" idea; the letter to the Hebrews keeps it almost entirely for Christ's single redemptive offering, while this word ranges more widely from an everyday count to the weightiest finality.
Nuances
The manuscripts place the word in different positions, so it is disputed whether it modifies "know" (yielding "you know once for all," the definitive sense that matches verse 3) or "saved" (yielding "the Lord who once saved the people out of Egypt," which can be read as a plain count).
- majorityThe word goes with "saved," the placement printed in the standard critical text of the Greek New Testament.; B. Metzger, A Textual Commentary on the Greek New Testament, on Jude 5
- minorityThe word goes with "know" ("you know once for all"), parallel to verse 3; scribes uneasy about applying so weighty a word to the readers' knowledge moved it to the verb "saved."; R. Bauckham, Jude, 2 Peter (WBC 50, 1983), on Jude 5; T. Wasserman, The Epistle of Jude: Its Text and Transmission (ConBNT 43, 2006)
Disputed
How much significance the definitive "once for all" sense carries in Hebrews, and whether the strengthened form ephapax is a genuinely different word or the same word intensified.
- majorityEphapax is a strengthened form of the same word, and the "once for all" force is contextual emphasis decided by what the word is applied to rather than a change in meaning; the two forms are functionally synonymous.; H. Attridge, Hebrews (Hermeneia, 1989); G. Cockerill, The Epistle to the Hebrews (NICNT rev., 2012)
- minorityThe contrast between the single act and the many repeated sacrifices activates a philosophical one-versus-many framework, so Christ's singular act carries ontological rather than merely numerical weight.; J. W. Thompson, 'EPHAPAX: The One and the Many in Hebrews,' NTS 53 (2007): 566-581
- minorityRepetition in the letter is not uniformly negative; the yearly rite's "once" anticipates Christ's single act typologically rather than simply opposing it, and the singularity-plurality contrast should not be over-generalized.; N. J. Moore, Repetition in Hebrews (WUNT II/388, 2015)