Just as we have numerical terms to indicate how often something occurred (i.e., once, twice, etc.), so there is in Greek. Paul said he was stoned “once” (2 Cor. 11:25); the high priest went into the Most Holy Place “once” every year (Heb. 9:7); it is appointed for man “once” to die (Heb. 9:27). But this Greek word for “once” (hapax) also has a stronger, more decisively unique usage, when it means not just “once” but “once for all.”
As a sacrifice under the Old Covenant, Jesus would have had to suffer “often,” but now “once” (and it could be, “once for all”) “at the end of the ages, He has appeared to put away sin by the sacrifice of Himself” (Heb. 9:26). Even more emphatically is the usage in Jude 3, which speaks of “the faith which was once for all delivered to the saints.”
Christ’s death for us was “once for all” – it will not and needs not happen again. The complete revelation of the will of God was “once for all” – it will not and needs not happen again.