What does 2 Timothy 1:12 mean?
Paul's suffering under persecution was due to his work as a preacher, apostle, and teacher (2 Timothy 1:11). Yet, he was "not ashamed" (Romans 1:16). Paul provides two reasons to explain why he was not reluctant to suffer for Christ. First, he could suffer for the sake of Jesus, because he knew Jesus, and Jesus' suffering gave Paul power to endure all things (Philippians 4:13).Second, Paul said he was not ashamed to suffer because he trusted Christ to be the ultimate foundation, not his own efforts. There is some uncertainty about what Paul is referring to when he says that Christ "is able to guard until that Day what has been entrusted to me." However, this particular reference to a "day" is most likely a reference to the moment after death when Paul would give account of his work before Christ (1 Corinthians 3:13; 2 Corinthians 5:9–10). This is also supported by 2 Timothy 1:18 where Paul will say of Onesiphorus, "May the Lord grant him to find mercy from the Lord on that Day!" There, too, Paul refers to the moment where a believer stands before the Lord.
Some translations use a capital D for "day." This reflects a slightly different interpretation. If this is the capital-d-"Day," then this means the "Day of the Lord," or the moment when Jesus will return in ultimate victory (Revelation 6:17; 16:14).