I think the use of amanuenses explains a lot, but I want to offer another perspective on this issue. I have been a professional writer for nearly twenty years, a time span not that far off from the career lengths of Apostles such as Paul and Peter. While I certainly am not in the same category as the Apostles, I do hold at least one thing in common with them—like them, I am a writer. By God’s grace, I have written many words for Ligonier Ministries, most of them for Tabletalk magazine.
As I think about my own writing career, I can make some observations about my own writing that might be instructive for how we view the issue of pseudonymous authorship and the New Testament. Occasionally, I look back on things I wrote many years ago, and while there are many similarities between my writing then and my writing now, there are also some key differences. First, there is the issue of vocabulary. Over the years, I have noticed an effort to vary my vocabulary more today than I did when I first started writing. I reach for a thesaurus more often now than I did back then. I am sure I could use one more often than I do, but the point is that you are going to find words in my writing now that you would not have found when I first started.
Stylistically, I have also noticed changes over the years. I still remember the occasion, many years ago, when one reader remarked to me that I was using a lot of long sentences in my writing. Since that time, I have consciously attempted to use shorter phrases in my writing. Do long sentences still appear from time to time? Sure. But the point is that I often try to use sentences that are more concise, whereas I was not so concerned about that when I first started writing.
Furthermore, over the years I have grown in my knowledge of theology and have tried to be more conscious of the audiences to whom I am writing. I sometimes explain concepts in a way that is different from what I once did, or at least I try to make the same point in different ways. You are going to find some differences in how I explain things today from how I explained them many years ago. The meaning will be the same, but I might put things a different way.
I could multiply examples of how I have changed in my writing over the years. The point is that I and my writing have changed. So this author’s perspective on biblical pseudonymity is this: If I can make such an effort to vary and change my style, why not the Apostles? True, I am not inspired as they were. However, our doctrine of inspiration does not say that the Apostles were mere automatons taken over by the Holy Spirit to give us the Scriptures. God used their giftings, desires, stylistic choices, and so on in giving us His Word. Surely they could have made conscious choices to vary their writing styles and to use different turns of phrases over their writing careers as well.
Same Author, Varied Corpus
I was not there when the Apostles wrote their letters, and I admit that I am engaging in a bit of conjecture. Still, I do not think it is speculating too much to think that the Apostles likely varied their writing styles intentionally over time according to their audiences and in line with their own maturation as writers. This would account for some of the variety we see among the biblical books that all claim the same author. From this author’s perspective, it is entirely reasonable to think that if my writing exhibits some change over time even though it is all written by the same author, so too could the Apostolic correspondence.