The source and ground of our distractive thoughts is the fragmented state of our memory. The memory was originally simple and one-pointed, but as a result of the fall its natural powers have been perverted: it has lost its recollectedness in God and has become compound instead of simple, diversified instead of one-pointed.
We recover the original state of our memory by restoring it to its primal simplicity, when it will no longer act as a source of evil and destructive thoughts. For Adam’s disobedience has not only deformed into a weapon of evil the soul’s simple memory of what is good; it has also corrupted all its powers and quenched its natural appetite for virtue. The memory is restored above all by constant mindfulness of God consolidated through prayer, for this spiritually elevates the memory from a natural to a supranatural state.
~St Gregory of Sinai
Prayerful Life 