Hebrews 5:13-14

Hebrews 5:13-14 give the reason why the further teaching is hard to explain.

For every one who useth milk (takes it as his ordinary food, and can digest nothing else) is unskilled (literally, inexperienced) in the word of righteousness; not in the Gospel as the true and righteous word (Grotius, Brown, and others); not in rightly ordered speech (Delitzsch); not quite the word of righteousness, as Melchisedec is king of righteousness, as if there were a play upon the words (Bleek); but rather, that message, that Gospel of which righteousness, imputed and imparted, in its double form of justification and holiness, is the central truth. The man who fails to see the spiritual significance of the law, or, having once seen it, goes back to his old condition of imperfect vision, neither knows the burden of human guilt and the consequent need of Divine atonement, nor the necessity of true holiness.

For he is a babe (an infant), and takes the same place among spiritual seers as an infant takes in the perception of worldly interests.

Hebrews 5:14. But solid food belongs to the full grown, to the spiritually mature (so the word often means in Greek writers). It is the same word in Hebrews 6:1 (‘let us go on unto perfection '). Then follows the description of them.

Even those who by reason of (by virtue of, not by means of) use (their long use, their habit) have their senses (properly their organs of sense, i.e the inner organs of the soul) exercised (by spiritual gymnastics; only it is healthy work also, and not play; comp. 1 Timothy 4:7, and Hebrews 12:11) to discern (literally, ‘with the view to discriminate between') good and evil. To discern what is good and noble and what is bad and mischievous. The child is easily imposed upon: he may be induced to take even poison if it is sweetened.to his taste; but a man has learnt by the discrimination which practice gives to make a distinction between things which differ, to ‘refuse the evil and choose the good,' the very discrimination in which children fail (Deuteronomy 1:39; Isaiah 7:16).

To have time for learning, time which is rich in lessons, and make no progress, is itself retrogression. Growth is the condition of all healthy life, physical, mental, spiritual. Not to grow in grace is to become dull and feeble; it is to retain in the system what ought to be replaced by new or added knowledge or feeling. It makes men specially susceptible to disease, and is the sure precursor of decay. The apostolic guard against apostasy is here and elsewhere to grow in grace and in the knowledge of Jesus Christ (2 Peter 3:18).