Hebrews 5:14

"But strong meat belongeth to them that are of full age, even them who by reason of use have their senses exercised to discern both good and evil." Those had not "their senses exercised," nor did they "know good and evil." He is not speaking now concerning life and conduct, when he says "to discern good and evil," for this is possible and easy for every man to know, but concerning doctrines that are wholesome and sublime, and those that are corrupted and low. The babe knows not how to distinguish bad and good food. Oftentimes at least it even puts dirt into its mouth, and takes what is hurtful; and it does all things without judgment; but not so the full grown man. Such babes are they who lightly listen to everything, and give up their ears indiscriminately: which seems to me to blame these Hebrews also, as being lightly "carried about," and now giving themselves to these, now to those. Which he also hinted near the end of the Epistle, saying, "Be not carried aside by divers and strange doctrines." This is the meaning of "to discern good and evil." "For the mouth tasteth meat, but the soul trieth words." Let us then learn this lesson. Do not, when thou hearest that a man is not a Heathen nor a Jew, straightway believe him to be a Christian; but examine also into all the other points; for even Manichaeans, and all the heresies, have put on this mask, in order thus to deceive the more simple. But if we "have the senses" of the soul "exercised to discern both good and evil," we are able to discern such teachers. But how do our "senses" become "exercised"? By continual hearing; by experience of the Scriptures. For when we set forth the error of those Heretics, and thou hearest today and to-morrow; and provest that it is not right, thou hast learnt the whole, thou hast known the whole: and even if thou shouldest not comprehend to-day, thou wilt comprehend to-morrow. "That have," he says, their "senses exercised." Thou seest that it is needful to exercise our hearing by divine studies, so that they may not sound strangely. "Exercised," saith he, "for discerning," that is, to be skilled.