The canonicity of this Epistle has never been questioned by the Church; and the testimony to its early and general use is in no way deficient. There are quite clear traces of its language in Clement of Rome, Ignatius, Polycarp, Justin Martyr, The Acts of Paul and Thecla, and Theophilus of Antioch. The letter is included in all the MSS., the old Versions and the Lists of the Pauline Epistles. The Muratorian Fragment names it as a production of Paul, and from the end of the second century it is quoted by name.
The Epistle has some permanent doctrinal value as containing the most important proof-passage for the inspiration of Scripture, 3:16, and also abiding historical significance in that it contains the clearest Scriptural testimony to the life of Paul after his first Roman imprisonment. Its main interest is one of character, and two portraits emerge from it. We have (1) the portrait of the ideal Christian minister, busily engaged in the work of his Master, confessing His Name, proclaiming His truth, shepherding His fold, defending his heritage, and battling with the powers of evil; and (2) the portrait of the Christian minister, with his work done, facing death. He acquiesces gladly in the present, but his eyes are turned mainly to the past or to the future. He is thankful for the work he was permitted to do, and serenely awaits the day of his crowning.
Christopher M. Date (2016) "By Command of God Our Savior: A Defense of the Pauline Authorship of the Pastoral Epistles," Diligence: Journal of the Liberty University Online Religion Capstone in Research and Scholarship: Vol. 1: Iss. 1 , Article 5.