Jamieson, Fausset and Brown on Titus 1:15

15. all things--external, "are pure" in themselves; the distinction of pure and impure is not in the things, but in the disposition of him who uses them; in opposition to "the commandments of men" (Tit 1:14), which forbade certain things as if impure intrinsically. "To the pure" inwardly, that is, those purified in heart by faith (Ac 15:9; Ro 14:20; 1Ti 4:3), all outward things are pure; all are open to, their use. Sin alone touches and defiles the soul (Mt 23:26; Lu 11:41).

nothing pure--either within or without (Ro 14:23).

mind--their mental sense and intelligence.

conscience--their moral consciousness of the conformity or discrepancy between their motives and acts on the one hand, and God's law on the other. A conscience and a mind defiled are represented as the source of the errors opposed in the Pastoral Epistles (1Ti 1:19; 3:9; 6:5).