I have fought the good fight Because it is customary to form a judgment from the event, Paul's fight might have been condemned on the ground that it did not end happily. He therefore boasts that it is excellent, whatever may be the light in which it is regarded by the world. This declaration is a testimony of eminent faith; for not only was Paul accounted wretched in the opinion of all, but his death also was to be ignominious. Who then would not have said that he fought without success? But he does not rely on the corrupt judgments of men. On the contrary, by magnanimous courage he rises above every calamity, so that nothing opposes his happiness and glory; and therefore he declares "the fight which he fought" to be good and honorable. I have finished my course He even congratulates himself on his death, because it may be regarded as the goal or termination of his course. We know that they who run a race have gained their wish when they have reached the goal. In this manner also he affirms that to Christ's combatants death is desirable, because it puts an end to their labors; and, on the other hand, he likewise declares that we ought never to rest in this life, because it is of no advantage to have run well and constantly from the beginning to the middle of the course, if we do not reach the goal. I have kept the faith [1] This may have a twofold meaning, either that to the last he was a faithful soldier to his captain, or that he continued in the right doctrine. Both meanings will be highly appropriate; and indeed he could not make his fidelity acceptable to the Lord in any other way then by constantly professing, the pure doctrine of the gospel. Yet I have no doubt that he alludes to the solemn oath taken by soldiers; as if he had said that he was a good and faithful soldier to his captain.

Footnotes

1 - "This word Faith' may indeed be taken for Fidelity; as if he had said that he was loyal to our Lord Jesus Christ, and that he never flinched, that he always performed what belonged to his office. But we may also take this word faith in its ordinary meaning, that Paul did not turn aside from the pure simplicity of the gospel, and even that he relied on the promises of salvation which had been given to him, and, having preached to others, shewed that he was in earnest in what he spoke. For, indeed, all the loyalty which God demands from us proceeds from our adhering firmly to his word, and being founded on it in such a manner that we shall not be moved by any storm or tempest that may arise." -- Fr. Ser.

I have fought a good fight - The Christian life is often represented as a conflict, or warfare; see the notes on 1-Timothy 6:12. That noble conflict with sin, the world, the flesh, and the devil, Paul now says he had been able to maintain.
I have finished my course - The Christian life, too, is often represented as a "race" to be run; compare the notes at 1-Corinthians 9:24-26.
I have kept the faith - I have steadfastly maintained the faith of the gospel; or, have lived a life of fidelity to my Master. Probably the expression means that he had kept his plighted faith to the Redeemer, or had spent a life in faithfully endeavoring to serve his Lord.

I have fought a good fight - Every reader will perceive that the apostle, as was his very frequent custom, alludes to the contests at the Grecian games: Τον αγυνα τον καλον ηγωνισμαι· I have wrestled that good wrestling - I have struggled hard, and have over come, in a most honorable cause.
I have finished my course - I have started for the prize, and have come up to the goal, outstripping all my competitors, and have gained this prize also.
I have kept the faith - As the laws of these games must be most diligently observed and kept, (for though a man overcome, yet is he not crowned, except he strive lawfully), so I have kept the rules of the spiritual combat and race; and thus, having contended lawfully, and conquered in each exercise, I have a right to expect the prize.

I have fought a good fight,.... The fight of faith; the same as in 1-Timothy 6:10; see Gill on 1-Timothy 6:10,
I have finished my course, or race; the race of life set before him, his course of years; his days were extinct, the grave was ready for him, and he for that; his last sands were dropping, and he was just going the way of all flesh; or else he means the course of his ministry, which he desired to finish with joy, and was now finishing; Acts 13:25 he was now got to the end of his line, to Rome, where he was to be a martyr for Christ, Acts 23:11 so that he now concluded his work was done, and his warfare accomplished:
I have kept the faith; by which he means, not so much the grace of faith, that was kept by Christ, the object, author, and finisher of it, and through his effectual grace and powerful intercession; but rather the profession of faith, which he had held fast without wavering; and chiefly the doctrine of faith, which was committed to his trust, which he had kept pure and incorrupt against all opposition; unless his faithfulness and integrity in the ministerial work should be thought rather to be intended; and which sense is favoured by the Syriac and Ethiopic versions, which render it, "I have kept my faith"; or have been faithful to my trust, as a good steward of the mysteries of God; not concealing and keeping back any thing that was profitable, but declaring the whole counsel of God; and now what remained for him was the crown of righteousness; and this he says for the comfort and encouragement and imitation of Timothy and others. The phrase seems to be Jewish; it is said (y) by the Jews, that he that does not keep the feast of unleavened bread, is as he who does not , "keep the faith of the holy blessed God".
(y) Zohar in Exod. fol. 51. 2.

"I have striven the good strife"; the Greek is not restricted to a fight, but includes any competitive contest, for example, that of the racecourse (1-Timothy 6:12 [ALFORD]; 1-Corinthians 9:24, &c.; Hebrews 12:1-2).
kept the faith--the Christian faith committed to me as a believer and an apostle (compare 2-Timothy 1:14; Revelation 2:10; Revelation 3:10).