Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled. Unto the pure all things are pure - This appears to have been spoken in reference to the Jewish distinctions of clean and unclean meats. To the genuine Christian every kind of meat proper for human nourishment is pure, is lawful, and may be used without scruple. This our Lord had long before decided. See on Luke 11:39-41 (note).
But unto them that are defiled - In their consciences, and unbelieving, απιστοις, unfaithful both to offered and received grace, nothing is pure - they have no part in Christ, and the wrath of God abides upon them. Their mind is contaminated with impure and unholy images and ideas, and their conscience is defiled with the guilt of sins already committed against God.