That thou keep this commandment - Referring particularly to the solemn injunction which he had just given him, to “fight the good fight of faith,” but perhaps also including all that he had enjoined on him.
Without spot - It seems harsh, and is unusual, to apply the epithet, “without spot” - ἄσπιλος aspilos - to a command or doctrine, and the passage may be so construed that this may be understood as referring to Timothy himself - “That thou keep the commandment so that thou mayest be without spot and unrebukable.” See Bloomfield, Crit. Dig., in loc. The word here rendered “without spot,” occurs in the New Testament only here and in James 1:27; 1Pe 1:19; 2 Peter 3:14. It means without any “stain” or “blemish; pure.” If applied here to Timothy, it means that he should so keep the command that there would be no stain on his moral character; if to the doctrine, that that should be kept pure.
Unrebukable - So that there be no occasion for reproach or reproof; see notes on Philippians 2:15.
Until the appearing of our Lord Jesus Christ - see notes on 1 Thessalonians 2:19; 1 Thessalonians 4:16; 1 Thessalonians 5:23.