John Calvin Commentary Hebrews 5:14

"But solid food is for fullgrown men, [even] those who by reason of use have their senses exercised to discern good and evil." — Hebrews 5:14 (ASV)

Of full age, or perfect, etc. He calls those perfect who are adults; he mentions them in opposition to babes, as is done in 1 Corinthians 2:6; 1 Corinthians 14:20; and Ephesians 4:13. For the middle and manly age is the full age of human life; but he figuratively calls those men in Christ—those who are spiritual.

And he would have all Christians to be such: those who by continual practice have attained a habit to discern between good and evil. For one cannot have been otherwise taught rightly in the truth, unless we are fortified by God’s protection against all the falsehoods and delusions of Satan; for on this account it is called the sword of the Spirit.

And Paul points out this benefit conferred by sound doctrine when he says, That we may not be carried about by every wind of doctrine (Ephesians 4:14). And truly, what sort of faith is that which doubts, being suspended between truth and falsehood? Is it not in danger of coming to nothing every moment?

But not satisfied to mention in one word the mind, he mentions all the senses, in order to show that we are always to strive until we are in every way equipped by God’s word, and are so armed for battle, that Satan may in no way steal upon us with his fallacies.

Thus it appears what sort of Christianity exists under the Papacy, where not only is the grossest ignorance praised under the name of simplicity, but the people are also most strictly prevented from seeking real knowledge.

Indeed, it is easy to judge by what spirit they are influenced—they who hardly allow that to be touched which the Apostle commands us to handle continually; they who imagine as praiseworthy a neglect which the Apostle here so severely reproves; they who take away the Word of God, the only rule for discerning rightly, a discernment which he declares to be necessary for all Christians!

But among those who are freed from this diabolical prohibition and enjoy the liberty of learning, there is still often no less indifference to both hearing and reading.

Thus, when we do not exercise our powers, we are stupidly ignorant and void of all discernment.