Exodus 3:12

A sign. Moses had modestly represented his own inability to perform so great a work, and such God generally selects. He encourages them therefore with a sign, to the splendour of which he was then a witness; and with another, which should appear in future, to convince him and all the world, that the undertaking was from God, when they should see him offering sacrifice in that place, out of the reach of Pharao, chap. xxiv. 3. Thus a future event is assigned to Achaz and Ezechias, as a sign of something that was to happen first. (Isaias vii; 4 Kings xix. 29.) Perhaps the sign here appointed is the presence of God enabling Moses to work miracles. (Menochius)