Vincent's NT Word Studies
8. Confirm. Compare ver. 6.Unto the end. Of the present aeon or period. See on end of the world, Matt. xxviii. 20.
Blameless (anegklhtouv). Used by Paul only. In apposition with you. Rev., unreprovable. The kindred verb ejgkalew occurs only in Acts and Romans. See on Rom. viii. 33. It means to accuse publicly, but not necessarily before a tribunal. See Acts xxiii. 28, 29; xxvi. 2, 7. Hence the word here points to appearance at God's bar.
Robertson's NT Word Studies
1:8 {Shall confirm} (bebaiwsei). Direct reference to the same word in verse #6. The relative hos (who) points to Christ. {Unto the end} (hews telous). End of the age till Jesus comes, final preservation of the saints. {That ye be unreproveable} (anegkletous). Alpha privative and egkalew, to accuse, old verbal, only in Paul in N.T. Proleptic adjective in the predicate accusative agreeing with humas (you) without hwste and the infinitive as in #1Th 3:13; 5:23; Php 3:21. "Unimpeachable, for none will have the right to impeach" (Robertson and Plummer) as Paul shows in #Ro 8:33; Col 1:22,28.