1 Peter 3:18

Here, I. The example of Christ is proposed as an argument for patience under sufferings, the strength of which will be discerned if we consider the several points contained in the words; observe therefore, 1. Jesus Christ himself was not exempted from sufferings in this life, though he had no guilt of his own and could have declined all suffering if he had pleased. 2. The reason or meritorious cause of Christ's suffering was the sins of men: Christ suffered for sins. The sufferings of Christ were a true and proper punishment; this punishment was suffered to expiate and to make an atonement for sin; and it extends to all sin. 3. In the case of our Lord's suffering, it was the just that suffered for the unjust; he substituted himself in our room and stead, and bore our iniquities. He that knew no sin suffered instead of those that knew no righteousness. 4. The merit and perfection of Christ's sacrifice were such that for him to suffer once was enough. The legal sacrifices were repeated from day to day, and from year to year; but the sacrifice of Christ, once offered, purgeth away sin, Heb 7:27; Heb 9:26, Heb 9:28; Heb 10:10, Heb 10:12, Heb 10:14. 5.

— Matthew Henry's Concise Commentary (public domain)

Confirmation of Pe1 3:17, by the glorious results of Christ's suffering innocently. For--"Because." That is "better," Pe1 3:17, means of which we are rendered more like to Christ in death and in life; for His death brought the best issue to Himself and to us [BENGEL]. Christ--the Anointed Holy One of God; the Holy suffered for sins, the Just for the unjust. also--as well as yourselves (Pe1 3:17). Compare Pe1 2:21; there His suffering was brought forward as an example to us; here, as a proof of the blessedness of suffering for well-doing. once--for all; never again to suffer. It is "better" for us also once to suffer with Christ, than for ever without Christ We now are suffering our "once"; it will soon be a thing of the past; a bright consolation to the tried. for sins--as though He had Himself committed them. He exposed Himself to death by His "confession," even as we are called on to "give an answer to him that asketh a reason of our hope." This was "well-doing" in its highest manifestation. As He suffered, "The Just," so we ought willingly to suffer, for righteousness' sake (Pe1 3:14; compare Pe1 3:12, Pe1 3:17). that he might bring us to God--together with Himself in His ascension to the right hand of God (Pe1 3:22). He brings us, "the unjust," justified together with Him into heaven.

— Jamieson-Fausset-Brown Commentary (public domain)