Protestants, as their name suggests, don't recognize the authority of the Pope. So it's not surprising that they don't recognize the Pope's infallible interpretation of Isaiah 53 as not involving Penal Substitution. In this post, I'll show the Papal commentary on this crucial passage, which was actually written quite a few decades back by a prior Pope but is still as valid today.
18 Servants, be subject to your masters with all respect, not only to the good and gentle but also to the unjust. 19 For this is a gracious thing, when, mindful of God, one endures sorrows while suffering unjustly. 20 For what credit is it if, when you sin and are beaten for it, you endure? But if when you do good and suffer for it you endure, this is a gracious thing in the sight of God. 21 For to this you have been called, because Christ also suffered for you, leaving you an example, so that you might follow in his steps. 22 He committed no sin, neither was deceit found in his mouth. [Isaiah 53:9] 23 When he was reviled, he did not revile in return; when he suffered, he did not threaten [cf Isaiah 53:7], but continued entrusting himself to him who judges justly. 24 He himself bore our sins [Isaiah 53:11] in his body on the tree, that we might die to sin and live to righteousness. By his wounds you have been healed. [Isaiah 53:5] 25 For you were straying like sheep [Isaiah 53:6], but have now returned to the Shepherd and Overseer of your souls.
Those are the words of St Peter himself, from the 2nd chapter of his First Epistle. He is speaking directly on Isaiah 53, showing how it's to be understood, giving practical illustrations.
What the Pope is saying here is that when it comes to suffering, it's clearly a bad thing in itself (being a product of original sin). But enduring unjust suffering has a meritorious quality about it, since you're suffering for the noble purpose of serving God and exemplifying love of neighbor. It is the patient enduring of unjust suffering that is how the Pope describes how "Christ suffered for you" (v21), and that this was to be an example for how we should patiently endure suffering.
For Protestants who see the Cross as a situation where Jesus suffered the Father's wrath in our place, this talk by the Pope makes little sense. In fact, I'm not surprised that every time I bring up this text in context that Protestants ignore the overall message. But this context is precisely how the Pope quotes and interprets Isaiah 53, not as a matter of suffering the Father's wrath, but rather suffering persecution at the hands of wicked men. The only thing Protestants can really do is fixate on an incorrect interpretation of verse 24, thinking that to "bear sins" means to have the Father punish Jesus in our place, but that's not what this phrase means nor does the context support it.
Since there were no chapters in the original text of the Pope's letter, there's no need to cut off the thought at the end of chapter 2, since the Pope continues on with the same theme:
3:1 Likewise, wives, be subject to your own husbands, so that even if some do not obey the word, they may be won without a word by the conduct of their wives, 2 when they see your respectful and pure conduct.
Continuing with the "be subject to" theme, the Pope gives the example of how a woman properly submitting to the unjust treatment of her husband can by her humility win her husband to Christ. The Pope went onto summarize: "Do not repay evil for evil or reviling for reviling, but on the contrary, bless, for to this you were called, that you may obtain a blessing ... But even if you should suffer for righteousness' sake, you will be blessed." (v9,14). Note how the phrase "for this you were called" appears also in 2:21, again teaching that not repaying evil for evil is how you gain God's favor. This is identical to what Our Lord taught on the Sermon on the Mount: "Blessed are those who are persecuted for righteousness' sake" (Mt 5:10). Jesus Himself was Blessed because we was persecuted for righteousness' sake.
Indeed, this "let those who suffer according to God's will entrust their souls to a faithful Creator while doing good" (4:19) theme is found throughout the Pope's Letter, since "God opposes the proud but gives grace to the humble" (1 Pt 5:5-6). Clearly there is a plain and united theme about meritorious suffering running throughout, none of which involves suffering God's wrath.
So the question is, are Protestants going to listen to the Pope as to what Isaiah 53 really means?