John Cassian, The Institutes XII.23: How perfection can only be attained through the virtue of humility

And so it is clearly shown that none can attain the end of perfection and purity, except through true humility, which he displays in the first instance to the brethren, and shows also to God in his inmost heart, believing that without His protection and aid extended to him at every instant, he cannot possibly obtain the perfection which he desires and to which he hastens so eagerly.