Verse 14. "But strong meat" - The high and sublime doctrines of Christianity; the atonement, justification by faith, the gift of the Holy Ghost, the fullness of Christ dwelling in the souls of men, triumph in and over death, the resurrection of the body, the glorification of both body and soul in the realms of blessedness, and an endless union with Christ in the throne of his glory. This is the strong food which the genuine Christian understands, receives, digests, and by which he grows.
"By reason of use" - Who, by constant hearing, believing, praying, and obedience, use all the graces of God's Spirit; and, in the faithful use of them, find every one improved, so that they daily grow in grace, and in the knowledge of Jesus Christ our Lord.
"Have their senses exercised" - The word aisqhthria signifies the different organs of sense, as the eyes, ears, tongue, and palate, nose, and finger ends, and the nervous surface in general, through which we gain the sensations called seeing, hearing, tasting, smelling, and feeling. These organs of sense, being frequently exercised or employed on a variety of subjects, acquire the power to discern the various objects of sense: viz. all objects of light; difference of sounds; of tastes or savours; of odours or smelling; and of hard, soft, wet, dry, cold, hot, rough, smooth, and all other tangible qualities.
There is something in the soul that answers to all these senses in the body.
And as universal nature presents to the other senses their different and appropriate objects, so religion presents to these interior senses the objects which are suited to them. Hence in Scripture we are said, even in spiritual things, to see, hear, taste, smell, and touch or feel. These are the means by which the soul is rendered comfortable, and through which it derives its happiness and perfection.
In the adult Christian these senses are said to be gegumnasmena, exercised, a metaphor taken from the athletae or contenders in the Grecian games, who were wont to employ all their powers, skill, and agility in mock fights, running, wrestling, &c., that they might be the better prepared for the actual contests when they took place. So these employ and improve all their powers, and in using grace get more grace; and thus, being able to discern good from evil, they are in little danger of being imposed on by false doctrine, or by the pretensions of hypocrites; or of being deceived by the subtleties of Satan. They feel that their security depends, under God, on this exercise-on the proper use which they make of the grace already given them by God. Can any reader be so dull as not to understand this?