This article is going to be a quickie. We all know the account of Jesus' agony in the Garden of Gethsemane (Mt 26:36-46), where Jesus prays, "My Father, if it be possible, let this cup pass from me; nevertheless, not as I will, but as you will." In order to support their erroneous doctrine of Penal Substitution, many Protestants have incorrectly assumed that this "cup" must be the 'cup of God's wrath' spoken about a few times in the Old Testament, particularly in Isaiah and Jeremiah (e.g. Jer 25:15). But this is easily disproved.
The key text to look to is Mark 10:38-39,
37 And they said to him, “Grant us to sit, one at your right hand and one at your left, in your glory.” 38 Jesus said to them, “You do not know what you are asking. Are you able to drink the cup that I drink, or to be baptized with the baptism with which I am baptized?” 39 And they said to him, “We are able.” And Jesus said to them, “The cup that I drink you will drink, and with the baptism with which I am baptized, you will be baptized, 40 but to sit at my right hand or at my left is not mine to grant, but it is for those for whom it has been prepared.”
This is the time when James and John request to be honored by sitting at the Lord's right and left in the Kingdom. Jesus responds by saying that this is no small honor, and in fact it comes at a hefty price. Jesus asks them if they will be able to drink the same cup and undergo the same baptism He is about to undergo. This is undoubtedly the same "cup" of Gethsemane. But what Jesus says completely undermines the Penal Substitution reading, since Jesus isn't drinking it in their place, but rather inviting them to drink it as well! The only acceptable reading is that this "cup" is physical persecutions that God's servants must endure, which explains why the Apostles were martyred. Thus, the 'cup of God's wrath in our place' thesis is instantly and elegantly disproved.
There's no way this "cup" could be the Eucharistic cup, and there's no way to read this as Jesus draining the wrath from the cup so that it can be drunk like sweet wine, since both of these require no heroic or challenge about them. (I've actually had Protestants make these kinds of claims.) This is further supported by the fact Jesus speaks of a "baptism" He will endure, which cannot be a water baptism since that already happened. Only the most desperate folks will deny the "cup" and "baptism" here refer to the same thing, physical persecutions.
And even with all that said, the "cup of God's wrath" in the Old Testament was that of physical persecutions as well, and Jeremiah 49:12 gives an interesting insight on the matter: "If those who did not deserve to drink the cup must drink it, will you go unpunished? You shall not go unpunished, but you must drink." This text shows that surrounding nations who were not deserving of the conquering armies had to suffer at their hands, and this corresponds to the fact sometimes God sends sweeping judgments across areas that sometimes include innocent people. The point isn't that these innocent people were taking wrath in place of the guilty, but rather along with. So in this sense, we could also say that Jesus suffered along with us in virtue of His humanity, without suggesting it was in place of us. And the Bible is very clear that Christians suffer for the kingdom, they're not exempt!
I've never been sure how Protestantism can address the fact that if Jesus suffered and died for us that we still have to suffer and die. That apparently disproves PSub in itself.