Titus 1:15 - Matthew Poole's English Annotations on the Holy Bible

Unto the pure all things are pure: by the pure here (as appeareth by the terms opposed to it) are meant all those whose hearts are purified by faith, working by love in a holy life. To these he saith all things, that is, all the creatures of God, all meats and drinks, are pure. What God hath cleansed none ought to call common or impure, Acts 10:14; so as, notwithstanding any law of God to the contrary, any believers under the gospel may eat of any meats. But unto them that are defiled and unbelieving is nothing pure; but if men be unbelievers, and so defiled, having not their hearts purified by faith, Acts 15:9, nothing is pure to them. But even their mind and conscience is defiled; their mind, their notion and understanding, is defiled; and their conscience, which is the practical judgment they make up about things, is defiled: if they forbear to eat, they are defiled through superstition; if they do eat, they sin by acting against the dictate of their conscience, which is the proximate rule of men's actions.