Charles Ellicott Commentary 2 Timothy 2:1

"Thou therefore, my child, be strengthened in the grace that is in Christ Jesus." — 2 Timothy 2:1 (ASV)

You therefore, my son, be strong in the grace that is in Christ Jesus.—St. Paul, after the reference to the faithless Asiatics and the true loyal Onesiphorus, with which he interrupted his exhortation, turns again to Timothy. You therefore (oun), my son, considering what has taken place, be strong. It is as though he said, Imitate the one loyal follower, and make up to me for the faithless conduct of so many false friends.

“You, then, be strong,” but not as men understand strength or firmness; but you be strong “in the grace that is in Christ Jesus”—that is, be strong in the power of that inward sanctification which enables a person to will and to do according to what God has commanded, in the power of that inward sanctification which alone proceeds from Christ, and which will never be lacking for anyone who is in Christ; in other words, “Be strong in the Lord, and in the power of His might” (Ephesians 6:10).