1 Timothy 1:15

faithful--worthy of credit, because "God" who says it "is faithful" to His word (Co1 1:9; Th1 5:24; Th2 3:3; Rev 21:5; Rev 22:6). This seems to have become an axiomatic saying among Christians the phrase, "faithful saying," is peculiar to the Pastoral Epistles (Ti1 2:11; Ti1 4:9; Tit 3:8). Translate as Greek, "Faithful is the saying." all--all possible; full; to be received by all, and with all the faculties of the soul, mind, and heart. Paul, unlike the false teachers (Ti1 1:7), understands what he is saying, and whereof he affirms; and by his simplicity of style and subject, setting forth the grand fundamental truth of salvation through Christ, confutes the false teachers' abstruse and unpractical speculations (Co1 1:18-28; Tit 2:1). acceptation--reception (as of a boon) into the heart, as well as the understanding, with all gladness; this is faith acting on the Gospel offer, and welcoming and appropriating it (Act 2:41). Christ--as promised. Jesus--as manifested [BENGEL]. came into the world--which was full of sin (Joh 1:29; Rom 5:12; Jo1 2:2). This implies His pre-existence. Joh 1:9, Greek, "the true Light that, coming into the world, lighteth every man." to save sinners--even notable sinners like Saul of Tarsus. His instance was without a rival since the ascension, in point of the greatness of the sin and the greatness of the mercy: that the consenter to Stephen, the proto-martyr's death, should be the successor of the same! I am--not merely, "I was chief" (Co1 15:9; Eph 3:8; compare Luk 18:13).

— Jamieson-Fausset-Brown Commentary (public domain)