Titus 1:15

Unto the pure all things [are] pure:—Jesus said, Blessed [are] the pure in heart: for they shall see God (Matthew 5:8). In the "Jewish fables" just referred to were rigid regulations concerning foods and purifications. Hence Paul adds, "It is not food that makes one impure. To the pure all things are pure. When one is unbelieving and defiled, no food can make him pure".but unto them that are defiled and unbelieving [is] nothing pure; but even their mind and conscience is defiled. —When a man has an impure heart he has impure thoughts. When his thoughts are impure, his mind and conscience is defiled. When his mind and conscience is defiled his actions will be impure and nothing about him will be pure.The conscience has been likened to the umpire in a baseball game. It calls the play “safe” or “out” based on the rules that it has been taught. Therefore the conscience must be properly taught so that it can be a guide for the Christian to follow.