Christ’s death was truly substitutionary. This is seen in
(a) the use of the figure of a lamb (1 Peter 1:19), which would bring to the readers’ minds the substitutionary aspect of the Levitical sacrifices;
(b) the direct statement of 1 Peter 2:24, “He Himself bore our sins in His body on the cross”; and
(c) the use of huper (“the just for the unjust,” italics added) in 1 Peter 3:18, where it means “in place of,” as it does in Philemon 13, a nonatonement passage.
Further, Christ’s substitutionary death was conclusive, for He died “once for all” (1 Peter 3:18, hapax, not pote, which means “once” or “formerly”).
Christ’s substitutionary death was also effective, for it brought redemption (1 Peter 1:18). Here “redeemed” is a translation of lutroō, which means “to set free by payment of a ransom.”
Thus Christ’s work on the cross was completely effective in setting the sinner free.
Charles C. Ryrie, Biblical Theology of the New Testament (Dubuque, IA: ECS Ministries, 2005), 251–252.