The Greek text of 2 Tim. 1:3 according to Robert Estienne’s Textus Receptus (1550) states,
Χάριν ἔχω τῷ θεῷ ᾧ λατρεύω ἀπὸ προγόνων ἐν καθαρᾷ συνειδήσει ὡς ἀδιάλειπτον ἔχω τὴν περὶ σοῦ μνείαν ἐν ταῖς δεήσεσίν μου νυκτὸς καὶ ἡμέρας
On the Greek word πρόγονος, Christian Gottlob Wilke (translated by Joseph Henry Thayer) wrote,1
πρό-γονος, -ου, ὁ, (προγίνομαι), born before, older: Hom. Od. 9, 221; plur. ancestors, Lat. majores, (often so by Grk. writ. fr. Pind. down): ἀπὸ προγόνων, in the spirit and after the manner received from (my) forefathers [cf. ἀπό, II. 2 d. aa. p. 59 bot.], 2 Tim. 1:3; used of a mother, grandparents, and (if such survive) great-grandparents, 1 Tim. 5:4 [A. V. parents] (of surviving ancestors also in Plato, legg. 11 p. 932 init.).*
Wilke references his entry on the preposition ἀπό (II. 2 d. aa.):2
II. of Origin; whether of local origin, the place whence; or of causa origin, the cause from which.
2 of causal origin, or the Cause; and
d. of the efficient cause, viz. of things from the force of which anything proceeds, and of persons from whose will, power, authority, command, favor, order, influence, direction, anything is to be sought;
aa. in general: ...λατρεύω τῷ θεῷ ἀπὸ προγόνων after the manner of the λατρεία received from my forefathers [cf. W. 372 (349); B. 322 (277)], 2 Tim. 1:3.
Thayer cites other authorities, including Winer and Buttman.
Winer writes,3 4
Who are the πρόγονοι to whom the apostle Paul refers? Some might believe that he is speaking of the patriarchs, such as Abraham, Isaac, and Jacob, as he calls Abraham “our father” (ὁ πατήρ ἡμῶν cp. Rom. 4:12). While πατήρ is not identical to πρόγονος, it's not out of the realm of possibility. Another possibility, however, is that the apostle Paul would be referring to his immediate ancestors in the same way that he mentions Timothy”s immediate ancestors, his mother Eunice and grandmother Lois (2 Tim. 1:5).
1.Is Paul taking credit for how his forefathers worshipped God?
2.Should not the reverse be true (i.e., parents taking credit for child’s success seems logical to me instead of children taking credit for parent’s success)?
The apostle Paul is not taking credit for their worship, after all, how could he who was born after them have influenced their worship? Rather, the apostle Paul is simply saying that his ancestors also worshipped God in the same manner as himself. That is, they too were Jews. The apostle Paul did not see himself as an adherent of a new religion, but one who continued in “the way” (ἡ ὁδός) of his ancestors (Acts 24:14). Judaism (ὁ Ἰουδαϊσμός cp. Gal. 1:13) was not a human contrivance but the true form of worship in the apostle Paul’s eyes. He confessed, “I am a Pharisee, the son of a Pharisee...” (Acts 23:6) and “I am a man, a Jew...brought up in this city at the feet of Gamaliel, and taught according to the perfect manner of the paternal law (τοῦ πατρῴου νόμου), being zealous toward God, just as you all are today” (Acts 22:3).
1 p. 538
2 p. 59
3 p. 372, §4
4 The Latin word modo means “manner,” and the word instar means “resemblance.”
5 p. 322
Buttmann, Alexander. A Grammar of the New Testament Greek. Trans. Thayer, Joseph Henry. Andover: Draper, 1873.
Wilke, Christian Gottlob. A Greek-English Lexicon of the New Testament: Being Grimm Wilke’s Clavis Novi Testamenti. Trans. Thayer, Joseph Henry.Ed. Grimm, Carl Ludwig Wilibald. Rev. ed. New York: American Book, 1889.
Winer, George Benedikt. A Grammar of the Idiom of the New Testament. 7th ed. Andover: Draper, 1892.