Steady inner conviction, held without the divided pull of doubt, dissolves the great obstacle that stands between a person and spiritual realization. That obstacle is the ego, sitting like a mass of rock across the path, and meditation is what commands it to lift and drop into the churning waters below, where the emotions and the unconscious close over it. (In his fixed key the mountain is the higher realm of consciousness itself; here the verse's own order to remove it reads the immovable ego-mass being cleared.)
The withered fig comes first because the same power that stops the outer fruiting of religion also moves the inner weight. When belief is withdrawn from the carnal, church-fed mind, its leaves dry from the root; and the will that can wither that tree can also cast the ego down into feeling and be free of it.
Fig tree: the outer fruiting mind of religion, which dries up once belief is pulled back from its root.
Mountain: the massed ego, the rock of the lower self standing across the inner path.
Sea: the churning emotions and the unconscious, the deep that receives what is cast down.