John Gill

For they all saw him, and were troubled,.... Had it been only seen by one, it might have been thought a fancy, and the effect of mere imagination; but as every one saw it, it was out of all doubt that so it was, and which gave them the greater concern: and immediately he talked with them; as soon as they saw him, "that very moment", as the Syriac renders it; that so by hearing his voice their fears might be allayed: and saith unto them, be of good cheer, it is I, be not afraid; See Gill on Mat 14:27.