1 Be strong in the grace As he had formerly commanded him to keep, by the Spirit, that which was committed to him, so now he likewise enjoins him “to be strengthened in grace.” By this expression he intends to shake off sloth and indifference; for the flesh is so sluggish, that even those who are endued with eminent gifts are found to slacken in the midst of their course, if they be not frequently aroused.
Some will say: “Of what use is it to exhort a man to ‘be strong in grace,’ unless free-will have something to do in cooperation?” I reply, what God demands from us by his word he likewise bestows by his Spirit, so that we are strengthened in the grace which he has given to us. And yet the exhortations are not superfluous, because the Spirit of God, teaching us inwardly, causes that they shall not sound in our ears fruitlessly and to no purpose. Whoever, therefore, shall acknowledge that the present exhortation could not have been fruitful without the secret power of the Spirit, will never support free-will by means of it.
Which is in Christ Jesus. This is added for two reasons; to shew that the grace comes from Christ alone, and from no other, and that no Christian will be destitute of it; for, since there is one Christ common to all, it follows that all are partakers of his grace, which is said to be in Christ, because all who belong to Christ must have it.
My son. This kind appellation, which he employs, tends much to gain the affections, that the doctrine may more effectually obtain admission into the heart.