“For the death that He died, He died to sin once for all; but the life that He lives, He lives to God.” Romans 6:10
The Greek word “ephapax” translated “once” in this verse, actually means “once for all.” Christ did not have to die again and again, a new death for ever sinner. He died unto sin once for all, His death being sufficient to take away “the sin of the [whole] world” (John 1:29).
The word occurs only five times in the Bible. Out text is the first confirming that His once-for-all death for sin was sufficient forever; He now lives wholly “to God.” The second confirms the reality of this permanent resurrection. In Jewish law, a factual claim was considered confirmed by the principle that “by the mouth of two or three witnesses every fact may be confirmed” (Matt. 18:16). Paul recalls that the resurrected Christ “appeared to more than five hundred brethren at one time” (1 Cor. 15:6). Two or three would have sufficed by He had five hundred witnesses. These saw Him alive once for all, and their lives were forever changed.
The other three references are in Hebrews -
“Who does not need daily, like those high priests, to offer up sacrifices, first for His own sins and then for the sins of the people, because this He did once for all when He offered up Himself” Hebrews 7:27
“And not through the blood of goats and calves, but through His own blood, He entered the holy place once for all, having obtained eternal redemption” Hebrews 9:12
“By this will we have been sanctified through the offering of the body of Jesus Christ once for all” Hebrews 10:10
Once for all He died for sin, then with His own shed blood, He entered into the presence of the Father, sanctified us forever, and was raised from the dead by impeccable testimony, once for all.