A.T. Robertson Commentary Revelation 2:25

"Nevertheless that which ye have, hold fast till I come." — Revelation 2:25 (ASV)

Howbeit (πλην). Common after ουκ αλλο as a preposition with the ablative , but here a conjunction as in Php 1:18.

Hold fast (κρατησατε). First aorist active imperative of κρατεω, either ingressive (get a grip on) or constative (hold on as a single decisive effort). See present imperative κρατε in 3:11 (keep on holding).

Till I come (αχρ ου αν ηξω). Indefinite temporal clause with αχρ ου (until which time) with modal αν and either the future active indicative or the first aorist active subjunctive of ηκω (usual idiom with αχρ in Revelation as in 7:3; 15:8; 20:3,5).