I was browsing the first epistle of Timotheos, and I noticed that the apostle Paulos sometimes preceded a statement by the Greek phrase πιστὸς ὁ λόγος (cp. 1 Tim. 1:15), which may be translated as "the faithful statement" or "the faithful saying." Why does Paulos do this? What significance does this phrase have? Where and how often does he actually employ this phrase?
Where the phrase is used
Here are several places where the apostle Paul uses this phrase, usually translated by the ESV as "The statement is trustworthy":
(1Tim 1:15 [GNT]) πιστὸς ὁ λόγος καὶ πάσης ἀποδοχῆς ἄξιος, ὅτι Χριστὸς Ἰησοῦς ἦλθεν εἰς τὸν κόσμον ἁμαρτωλοὺς σῶσαι· ὧν πρῶτός εἰμι ἐγώ,
(1Tim 3:1 [GNT]) Πιστὸς ὁ λόγος· εἴ τις ἐπισκοπῆς ὀρέγεται, καλοῦ ἔργου ἐπιθυμεῖ.
(1Tim 4:9 [GNT]) πιστὸς ὁ λόγος καὶ πάσης ἀποδοχῆς ἄξιος,
(2Tim 2:11 [GNT]) πιστὸς ὁ λόγος· εἰ γὰρ συναπεθάνομεν, καὶ συζήσομεν·
(Titus 3:8 [GNT]) Πιστὸς ὁ λόγος, καὶ περὶ τούτων βούλομαί σε διαβεβαιοῦσθαι, ἵνα φροντίζωσιν καλῶν ἔργων προΐστασθαι οἱ πεπιστευκότες θεῷ. ταῦτά ἐστιν καλὰ καὶ ὠφέλιμα τοῖς ἀνθρώποις·
Why and what significance? (a start)
We can observe that the usage is in the "pastoral" epistles.
J.H. Bernard is helpful just with observations, in the Cabridge Greek Commentary Series while commenting on 1 Tim.1:15 [I've used theWord.net software, with these commentaries available here]:
Having recently read BDAG lexicon on πιστός, I think what Bernard writes here is a good start for this phrase.