…do not leave any part of your soul or body unwatched. In this way you will master the evil spirits that assail you and you will boldly present yourself to Him who examines hearts and minds (cf. Psalms 7:9); and He will not scrutinize you, for you will have already scrutinized yourself. As St Paul says, “If we judged ourselves we would not be judged” (1 Corinthians 11:31).
Then you will experience the blessing that David experienced, and you will say to God, “Darkness will not be darkness with Thee and night shall be bright as day for me, for Thou hast taken possession of my mind” (cf. Psalms 139:12-13). It is as if David were saying that not only has God become the sole object of his soul’s desire, but also that any spark of this desire in his body has returned to the soul that produced it, and through the soul has risen to God, hangs upon Him and cleaves to Him. For just as those who cleave to the perishable pleasures of the senses expend all the soul’s desire in satisfying their fleshly proclivities and become so entirely materialistic that the Spirit of God cannot abide in them (cf. Genesis 6:3), so in the case of those who have elevated their intellect to God, and who through divine longing have attached their soul to Him, the flesh is also transformed, is exalted with the soul, communes together with the soul in the Divine, and itself likewise becomes the possession and dwelling-place of God, no longer harboring any enmity towards Him or any desires that are contrary to the Spirit (cf. Galatians 5:17).
~St Gregory Palamas (Philokalia vol.4, p.339)
Prayerful Life 