He who devoutly strives to attain wisdom and is on his guard against the invisible powers, should pray that both natural discrimination - whose light is but limited - and the illuminating grace of the Spirit abide in him. The first by means of practice trains the flesh in virtue, the second illuminates the intellect so that it chooses above all else companionship with wisdom; and through wisdom it destroys the strongholds of evil and pulls down 'all the self-esteem that exalts itself against the knowledge of God' (II Cor. 10:5).