Whereas Isaiah 53:10 says that God put Christ to death, making His soul an offering for sin, verse 12 says that "He poured out His soul unto death." If Christ merely put Himself to death on the cross, and God did accept Him as an offering for sin, Christ's death would not have been a vicarious death for us; it would have been only martyrdom. Likewise, if God was pleased to put Him to death, and He was not willing to die, then His death would not have been a vicarious death. The vicarious death of Christ depends on God's being pleased to put Him to death and on Christ's being willing to die in such a way. Moreover, if Christ had sinned, His death could not be counted as a vicarious death; He would have had to die for Himself, and He could not have died for us.
Isaiah's writing in this chapter presents a clear defense in the heavenly court, testifying that God was pleased to put Christ to death, that Christ was willing to die for others, and that He was altogether sinless (v. 9). Thus, His death was truly a vicarious death.
Verse 12b says, "Because He poured out His soul unto death/And was numbered with the transgressors,/Yet He alone bore the sin of many / And interceded for the transgressors." While Christ was on the cross, He prayed for the ones who had crucified Him (Luke 23:34).
Isaiah 53:9 tells us, "They assigned His grave with the wicked,/But with a rich man in His death,/Although He had done no violence,/Nor was there any deceit in His mouth." This verse reveals that Christ was sinless and that His death was not for any sins of His own. If He had done any violence or if there had been deceit in His mouth, He would not have been sinless and He could not have died for us. Christ was altogether sinless. Because He had no sin, He did not need to die for Himself. His vicarious death was for us.