Jamieson, Fausset and Brown on 2 Timothy 1:12

12. For the which cause--For the Gospel cause of which I was appointed a preacher (2Ti 1:10, 11).

I also suffer--besides my active work as a missionary. Ellicott translates, "I suffer even these things"; the sufferings attendant on my being a prisoner (2Ti 1:8, 15).

I am not ashamed--neither be thou (2Ti 1:8).

for--Confidence as to the future drives away shame [Bengel].

I know--though the world knows Him not (Joh 10:14; 17:25).

whom--I know what a faithful, promise-keeping God He is (2Ti 2:13). It is not, I know how I have believed, but, I know WHOM I have believed; a feeble faith may clasp a strong Saviour.

believed--rather, "trusted"; carrying out the metaphor of a depositor depositing his pledge with one whom he trusts.

am persuaded--(Ro 8:38).

he is able--in spite of so many foes around me.

that which I have committed unto him--Greek, "my deposit"; the body, soul, and spirit, which I have deposited in God's safe keeping (1Th 5:23; 1Pe 4:19). So Christ Himself in dying (Lu 23:46). "God deposits with us His word; we deposit with God our spirit" [Grotius]. There is one deposit (His revelation) committed by God to us, which we ought to keep (2Ti 1:13, 14) and transmit to others (2Ti 2:2); there is another committed by God to us, which we should commit to His keeping, namely, ourselves and our heavenly portion.

that day--the day of His appearing (2Ti 1:18; 2Ti 4:8).