I charge thee (diamarturomai). Rather, “I testify.” See 1Th 4:6. See 1Ti 5:21 for this verb and appeal to God and Christ.
Who shall judge (tou mellontos krinein). “The one going or about to judge” (regular idiom with mellō). The quick and the dead (zōntas kai nekrous). “Living and dead.” See 1Th 4:16.
And by his appearing (kai tēn epiphaneian). Accusative of conjuration (verbs of swearing), after diamarturomai as is basileian (by his kingdom). See note on 1Th 5:27. For epiphaneian, see note on 1Th 1:10; Tit 2:13; 1Ti 6:14; 2Th 2:8.