And when Ambrose said this, he was speaking in that treatise which he wrote concerning Flight from the World, wherein he taught that this world was to be fled not by the body, but by the heart, which he argued could not be done except by God’s help. For he says: “We hear frequent discourse concerning fleeing from this world, and I would that the mind was as careful and solicitous as the discourse is easy; but what is worse, the enticement of earthly lusts constantly creeps in, and the pouring out of vanities takes possession of the mind; so that what you desire to avoid, this you think of and consider in your mind. And this is difficult for a man to beware of, but impossible to get rid of. Finally, the prophet bears witness that it is a matter of wish rather than of accomplishment, when he says, ‘Incline my heart to Thy testimonies, and not to covetousness.’ For our heart and our thoughts are not in our own power, and these, poured forth unexpectedly, confuse our mind and soul, and draw them in a different direction from that which you have proposed to yourself; they recall you to worldly things, they interpose things of time, they suggest voluptuous things, they inweave enticing things, and in the very moment when we are seeking to elevate our mind, we are for the most part filled with vain thoughts and cast down to earthly things.” Therefore it is not in the power of men, but in that of God, that men have power to become sons of God. Because they receive it from Him who gives pious thoughts to the human heart, by which it has faith, which worketh by love; for the receiving and keeping of which benefit, and for carrying it on perseveringly unto the end, we are not sufficient to think anything as of ourselves, but our sufficiency is of God, in whose power is our heart and our thoughts.
Reproduced in full. Translation: Nicene and Post-Nicene Fathers, series 1, vol. 5 (Schaff, 1887), public domain (Public domain).