Firm (stereos). Old adjective, solid, compact, in N.T. only here, 1Pe 5:9; Heb 5:12, Heb 5:14. See stereōma in Col 2:5. For themelios see note on 1Co 3:11; Rom 15:20; 1Ti 6:19. Cf. hedraiōma in 1Ti 3:15.
Seal (sphragis). See 1Co 9:2; Rom 4:11.
Knoweth (egnō). Timeless aorist active indicative of ginōskō. Quotation from Num 16:5.
Let every one depart (apostētō pās). Paraphrase of Num 16:27; Isa 26:13; Isa 52:11; Jer 20:9. Second aorist active imperative of aphistēmi (intransitive use), “Let every one stand off from.” Probably another echo of the rebellion of Korah.