By St. Maximus the Confessor
Jacob's well is Scripture.
The water is the spiritual knowledge found in Scripture.
The depth of the well is the meaning, only to be attained with great difficulty, of the obscure sayings in Scripture.
The bucket is learning gained from the written text of the word of God, which the Lord did not possess because He is the Word Himself; and so He does not give believers the knowledge that comes from learning and study, but grants to those found worthy the ever-flowing waters of wisdom that spill from the fountain of spiritual grace and never run dry. For the bucket - that is to say, learning - can only grasp a very small amount of knowledge and leaves behind all that it cannot lay hold of, however it tries. But the knowledge that is received through grace, without study, contains all the wisdom that man can attain, springing forth in different ways according to his needs.
From Philokalia, "Second Century of Various texts," II:193, 194.