Little children, love not the world, neither the things which are in the world. If any man love the world, the love of God is not in him: for everything that is in the world is the lust of the flesh and the lust of the eyes and the pride of life, which is not of the Father but of the world. And the world perisheth and the lust thereof: but he that doeth the will of God abideth forever (1 John 2:15-17).
The saints therefore scorn all those things on which the world exists, but it is impossible for them never to be carried away to them by a brief aberration of thoughts, and even now no man, except our Lord and Saviour, can keep his naturally wandering mind always fixed on the contemplation of God so as never to be carried away from it through the love of something in this world.
As Scripture says: “Even the stars are not clean in His sight,” and again: “If He puts no trust in His saints, and findeth iniquity in His angels,” or as the more correct translation has it: “Behold among His saints none is unchangeable, and the heavens are not pure in His sight.”
I should say then that the saints who keep a firm hold of the recollection of God and are borne along, as it were, with their steps suspended on a line stretched out on high, may be rightly compared to rope dancers, commonly called funambuli, who risk all their safety and life on the path of that very narrow rope.
[…] And while with marvellous skill they ply their airy steps through space, if they keep not their steps to that all too narrow path with careful and anxious regulation, the earth which is the natural base and the most solid and safest foundation for all, becomes to them an immediate and clear danger, not because its nature is changed, but because they fall headlong upon it by the weight of their bodies.
So also that unwearied goodness of God and His unchanging nature hurts no one indeed, but we ourselves by falling from on high and tending to the depths are the authors of our own death, or rather the very fall becomes death to the faller.
[…] Scripture says: “thine own wickedness shall reprove thee, and thy apostasy shall rebuke thee. Know thou and see that it is an evil and a bitter thing for thee to have left the Lord thy God;” for “every man is bound by the cords of his sins.” To whom this rebuke is aptly directed by the Lord: “Behold,” He says, “all you that kindle a fire, encompassed with flames, walk ye in the light of your fire and in the flames which you have kindled.”
John Cassian (c. 360-435): Conferences 23, 8-9.