Are Paul's later letters more detailed than his earlier ones?

Yes. Paul's later prison epistles—Ephesians, Colossians, and Timothy—set forth certain truths in greater detail than his earlier letters, such as Romans and Corinthians. His writings reflect a progressive revelation, with later epistles containing a fuller revelation than the early ones.

Les teaches that Paul experienced a progressive revelation, just as the Bible as a whole does. Some truths come out in greater detail in Paul's later prison epistles than in his first letter. Romans and Corinthians were pre-prison epistles containing revelations Paul received early on. Ephesians, Colossians, and Timothy were written toward the end of his career and contain a greater revelation. For example, Ephesians 1:9-10 reveals the secret of God's will, that in the dispensation of the fullness of time He might gather together in one all things in Christ, both in heaven and on earth. Les also notes that the mystery of the believer's change—being raised incorruptible or changed in a moment, in the twinkling of an eye—was not understood until the Lord revealed it to this apostle.

Why do some things in Paul's letters come out in greater detail in his later epistles?

Paul experienced progressive revelation, just as Scripture as a whole unfolds progressively. What he received earlier in pre-prison letters like Romans and Corinthians is expanded in later prison epistles such as Ephesians, Colossians, and Timothy, where he had a greater revelation toward the end of his writing career.