St Maximos the Confessor

Since man is composed of body and soul, he is moved by two laws, that of the flesh and that of the spirit (cf. Rom. 7:23).

The law of the flesh operates by virtue of the senses; the law of the Spirit operates by virtue of the intellect.

The first law, operating by virtue of the senses automatically binds one closely to matter; the second law, operating by virtue of the intellect, brings about direct union with God.

Suppose there is someone who does not doubt in his heart (cf. Mark 11:23) - that is to say, who does not dispute in his intellect - and through such doubt sever that immediate union with God which has been brought about by faith, but who is dispassionate or, rather, has already become god through union with God by faith: then it is quite natural that if such a person says to a mountain, ‘Go to another place’, it will go (cf. Matt. 17:20).

The mountain here indicates the will and the law of the flesh, which is ponderous and hard to shift, and in fact, so far as our natural powers are concerned; is totally immovable and unshakeable.

St Maximos the Confessor