15 To the pure all things are pure, but to those who are defiled and unbelieving nothing is pure; but even their mind and conscience are defiled.
16 They profess to know God, but in works they deny Him, being abominable, disobedient, and disqualified for every good work.
The words, “Unto the pure all things are pure,”are to be understood in their context, which speaks of arbitrary ascetic prohibitions. This is best understood as a maxim of the Judaic Gnostics, based on a perversion of Luke 11:41 where our Lord, speaking of the Pharisees and their man-made ceremonial washings says, “All things are clean to you.” The purity spoken of in our Titus reference speaks, not of purity which is the absence and opposite of immorality, etc., but of the ceremonial purity of man-made regulations. Our Lord tells the Jewish leaders that there is nothing wrong in eating with ceremoniously unwashed hands. that is, the person who does not subscribe to the Pharasaical regulations is not impure or defiled, nor is the food he eats affected in that way. Paul accepts the statement as a truth, but not in the intention of the speaker. Referring to those who are defiled; their moral obliquity is more characteristic of them than their intellectual perversion. the satisfaction of natural bodily desires (for it is these that are in question) is, when lawful, a pure thing, not merely innocent, in the case of the pure; it is an impure thing, even when lawful, in the case of “them that are defiled.” And for this reason: their intellectual apprehension of these things is perverted by defiling associations; “the light that is in them is darkness,” and their conscience has, from a similar cause, lost its sense of discriminating between what is innocent and what is criminal. That any action with which they themselves are familiar could be pure is inconceivable. — Wuest, pages 188-189
profess (v.16) = agree, confess belief in
disqualified (v.16) — The word adokimos literally signifies “not standing the test.” It isused in the Septuagint of Isaiah 1:22 of silver which has become dross, a mind of which God cannot approve. In 2 Corinthians 13:5-7 it is used with reference to the great test as to whether Christ is in a person, and in 2 Timothy 3:8 of those who are “reprobate concerning the faith,” i.e., those hose moral sense is perverted and whose minds are beclouded with their own speculations. In the present passage it implies that mere professors, if put to the test in regard to any good work, can only be rejected, and rejection by God is the inevitable result. — Vine, page 238.