I thank God, whom I serve with a clear conscience as did my forefathers, as I constantly remember you night and day in my prayers.
Paul asserts his apostolic authority not for Timothy's sake alone; Timothy already believed. He writes with these grand titles because he stands at death's door and means to seal his whole ministry with his blood, that the Church may know his doctrine comes from God Himself, not from a mortal man's opinion.
AI summary
Commenting on 2 Timothy 1:1-18
Here is, I. The inscription of the epistle Paul calls himself an apostle by the will of God, merely by the good pleasure of God, and by his grace, which he professes himself unworthy of. According to the promise of life which is in Christ Jesus, or according to the gospel.
Commenting on 2 Timothy 1:1-5
Verse 3. I thank God, whom I serve from my forefathers. Paul reckoned among his forefathers the patriarchs and the holy men of former times, as being of the same nation with himself; though it may be that he also included his more immediate ancestors, who, for anything known to the contrary, may have been distinguished examples of piety.