"One significant literary feature of this epistle (as well as of 2 Timothy and Titus) is the recurrence of the phrase “the saying is trustworthy” (1:15; 3:1; 4:9; cf. 2 Tim. 2:11; Titus 3:8). The purpose of this phrase is to call attention to the importance of the truth that Paul references. These phrases often serve as crisp summaries of the gospel and its implications for the life of the Christian. In this way, Paul helps Timothy grasp the central or core truths of the message that he is called to proclaim (cf. 4:13, 16).
Another significant literary feature is 3:16. Some scholars think Paul is quoting a creed that was circulating in the early church. Or, it could be that Paul is giving the church a creed. Paul introduces the successive and rhythmic phrases with the expression “we confess.” The phrases then offer a summary of the earthly life of Christ from the incarnation to the ascension.
Finally with respect to literary style, a brief word must be said about the vocabulary and syntax of the Pastoral Epistles. Those who deny that Paul wrote 1 Timothy, 2 Timothy, and Titus frequently point out that there are significant differences between the vocabulary of these three letters and the vocabulary of the rest of the Pauline corpus. The most basic form of the vocabulary-based argument against Pauline authorship of the Pastorals says that since these three letters contain many words not found in the other letters attributed to Paul, the Pastoral Epistles must be from a different author. This argument is flawed for several reasons. First, it assumes that a well-educated individual such as Paul had a limited vocabulary and was bound to use only a select set of words every time he wrote. This is not tenable. It would be quite easy to point to several modern books that are known to be written by the same author and find differences in vocabulary between them, but we would not then deny the common authorship of those books. The vocabulary Paul does use in the Pastoral Epistles was common in his era, so there is no reason to think he would not have known it. Furthermore, the vocabulary-based argument against Pauline authorship of the Pastoral Epistles is quite circular. Critical scholars who hold this position first assume—without really proving—that only a handful of letters are authentically Pauline and then attempt to disprove the Pauline authorship of the Pastorals based on that. Effectively, what happens is that critical scholars presuppose that Paul did not write the Pastorals and then conclude, based almost exclusively on that presupposition, that Paul did not write the Pastoral Epistles.
The vocabulary-based argument against Pauline authorship of the Pastoral Epistles is overstated and circular. Any differences between the Pastorals and the rest of Paul’s epistles are more easily explained by the fact that the addressees and circumstances of the Pastoral Epistles are different than the addressees and circumstances of Paul’s other epistles. The same applies in the case of syntactical differences between the Pastoral Epistles and Paul’s other letters. Moreover, Paul also likely used an amanuensis (secretary) to help him write the Pastorals who was not the same amanuensis that helped him write his other epistles. This would also explain some of the differences between the Pastoral Epistles and the rest of the Pauline letters."
The Reformation Study Bible (Orlando, FL: Reformation Trust Publishing, 2015), 2149, 2151-2152