Did Jesus die in our place, bearing the punishment for our sins? In Did the Earliest Christians Really Believe in Substitutionary Atonement (and Even Imputation)?, Dr. Michael J. Kruger writes:
The average internet-level narrative goes something like this: the earliest Christians had no clear understanding for why Jesus died on the cross and what it accomplished. The idea of a substitutionary atonement is a late invention designed to retroactively explain the (otherwise embarrassing) death of Jesus. In fact, it was not until Anselm’s Cur Deus Homo (Why the God-Man?) in the middle ages that someone came up with the idea that Jesus died in place of sinners.
Of course, such a narrative can be readily refuted just examining the writings of the New Testament itself–particular[ly] the letters of Paul. However, it is also worth noting that this view was held by some of the earliest Christian writers; in this case, by the author of the Epistle to Diognetus in the early second century. Here are some excerpts from the author that affirm key aspects of substitutionary atonement: