As a theology professor, I routinely hear people claim that Anselm invented the penal substitution view of the atonement. This is the idea that Jesus bore the punishment that we rightly deserved because of our sin, and that this was necessary for us to be reconciled to God.
Before Anselm, the church had a view that focused almost exclusively on ideas like victory—i.e. on the cross Jesus defeated the enemies of humanity like Satan, death, and sin—and healing—i.e. the entirety of his incarnate life healed our broken humanity and made it possible for us to resume the path to godlikeness. (If you’d like some examples, see here and here.)
And people often use the relative newness of the theory as a reason for rejecting it. If the early church didn't think of the cross as some kind of vicarious punishment, if that was just a medieval invention, let's get rid of it.
There's just one problem with this: it's wrong. And it's wrong for two important reasons.
1. Anselm Did Not Teach Penal Substitution
I'm not going to go into great detail here, but the key is that Anselm taught a view of the atonement that is more properly labeled the satisfaction theory of the atonement. Unlike penal substitution views, which tend to emphasize forensic ideas like guilt and punishment, Anselm's view revolves around the concept of honor. The purpose of the entire created realm, and every individual creature, is to offer glory to God. When humans sinned, they brought dishonor into the universe and undermined God's glory. In so doing, they fundamentally undermined not only their own well being but the well being of the entire universe.
In his famous Cur Deus Homo, Anselm explained why it was fitting for God to send his own Son in this situation, joining full deity and full humanity in a single person so that he might offer the true and proper human obedience that would bring glory to God and begin the process of restoring the order so obviously lacking in this broken world. Anselm clearly draws on the feudal image of the honor that a vassal owes his liege lord and how failure to render adequate honor fundamentally undermines the entire system. And whatever you think about this culturally-inspired way of explaining the atonement, it clearly differs from penal substitution in that although it is still a substitutionary model, it does not emphasize punishment at all.
2. Penal Substitution Existed Long Before Anselm
Despite claims to the contrary, it's not that difficult to find something akin to penal substitution in Christian theology long before Anselm. Even if the early church tended to place greater emphasis on motifs like victory and healing, many early theologians affirmed that Jesus in some way bore our punishment, which they typically referred to as the "curse" that was rightfully ours because of the guilt we have incurred through sin.
For example, Justin Martyr talks about all of humanity being under the curse because of their sin. According to him, though, Jesus took the curses and the corresponding suffering that was rightfully ours upon himself so that we might be redeemed (Dialogue with Trypho, 95). Although Justin doesn't use the explicit language of "punishment" here, it's hard to see why this would not qualify as a penal substitution view given that Jesus still (1) bears the suffering that we (2) should have rightfully endured so that (3) we might be redeemed. And similar sentiments are sprinkled throughout the church's early theology (e.g. Athanasius, Against the Arians, 13.9; Ambrose, On the Christian Faith, 9; Gregory the Great, Commentary on Job 3:14; 9:39; and although I haven't read it myself yet, I'm told that Theodore abu Qurra's That We Have Five Enemies contains an extended discussion of penal substitution).
I could offer more evidence, but it's not really necessary. The simple fact is that it's not hard to find some kind of penal substitution in the early church. They held other views of the atonement as well, of course, several of which were far more important to them than penal substitution. But they had no problem offering multiple perspectives on the atonement, and penal substitution fits just fine with the other things they wanted to say about the cross. And we also shouldn't confuse their approach to penal substitution with the more fully-developed theories that don't become common until after the Reformation (as far as I know). But just because they didn’t develop penal substitution with as much rigor as later theologians doesn't mean that the essential concepts are missing.
So What Does This All Mean?
At the very least, people need to stop critiquing/rejecting penal substitution as a "modern" development in theology. While contemporary penal substitution surely contains many aspects that are modern, the core has been around for a while.
And we should also drop the bogus claim that Anselm invented penal substitution. Not only is this historically wrong, but it causes us to miss to nuances of Anselm’s own approach. His emphasis on shame as a consequence of sin and the removal of shame through the atoning work of Christ is something that the modern, western world desperately needs to hear.