Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter XIII. On the lightness of thoughts.

Chapter XIII.

On the lightness of thoughts.

For when the mind has taken in the meaning of a passage in any Psalm, this insensibly slips p. 409 away from it, and ignorantly and thoughtlessly it passes on to a text of some other Scripture. And when it has begun to consider this with itself, while it is still not thoroughly explored, the recollection of some other passage springs up, and shuts out the consideration of the former subject. From this too it is transferred to some other, by the entrance of some fresh consideration, and the soul always turns about from Psalm to Psalm and jumps from a passage in the Gospels to read one in the Epistles, and from this passes on to the prophetic writings, and thence is carried to some spiritual history, and so it wanders about vaguely and uncertainly through the whole body of the Scriptures, unable, as it may choose, either to reject or keep hold of anything, or to finish anything by fully considering and examining it, and so becomes only a toucher or taster of spiritual meanings, not an author and possessor of them. And so the mind, as it is always light and wandering, is distracted even in time of service by all sorts of things, as if it were intoxicated, and does not perform any office properly. For instance, while it is praying, it is recalling some Psalm or passage of Scripture. While it is chanting, it is thinking about something else besides what the text of the Psalm itself contains. When it repeats a passage of Scripture, it is thinking about something that has to be done, or remembering something that has been done. And in this way it takes in and rejects nothing in a disciplined and proper way, and seems to be driven about by random incursions, without the power either of retaining what it likes or lingering over it. It is then well for us before everything else to know how we can properly perform these spiritual offices, and keep firm hold of this particular verse which you have given us as a formula, so that the rise and fall of our feelings may not be in a state of fluctuation from their own lightness, but may lie under our own control.