John Cassian, The Institutes VII.2: How dangerous is the disease of covetousness

But this disease coming upon us at a later period, and approaching the soul from without, as it can be the more easily guarded against and resisted, so, if it is disregarded and once allowed to gain an entrance into the heart, is the more dangerous to every one, and with the greater difficulty expelled. For it becomes “a root of all evils,” and gives rise to a multiplicity of incitements to sin.