A.T. Robertson Commentary 2 Timothy 2:19

"Howbeit the firm foundation of God standeth, having this seal, The Lord knoweth them that are his: and, Let every one that nameth the name of the Lord depart from unrighteousness." — 2 Timothy 2:19 (ASV)

Howbeit (μεντο). Strong adversative, "however."

Firm (στερεος). Old adjective, solid, compact, in N.T. only here, 1 Peter 5:9; Hebrews 5:12,14. See στερεωμα in Col 2:5. For θεμελιος see 1 Corinthians 3:11; Romans 15:20; 1 Timothy 6:19. Cf. εδραιωμα in 1 Timothy 3:15.

Seal (σφραγις). See 1 Corinthians 9:2; Romans 4:11.

Knoweth (εγνω). Timeless aorist active indicative of γινωσκω. Quotation from Nu 16:5.

Let every one depart (αποστητω πας). Paraphrase of Nu 16:27; Isaiah 26:13; 52:11; Jeremiah 20:9. Second aorist active imperative of αφιστημ (intransitive use), "Let every one stand off from." Probably another echo of the rebellion of Korah.