John 4:13

thirst again . . . never thirst, &c.--The contrast here is fundamental and all comprehensive. "This water" plainly means "this natural water and all satisfactions of a like earthly and perishable nature." Coming to us from without, and reaching only the superficial parts of our nature, they are soon spent, and need to be anew supplied as much as if we had never experienced them before, while the deeper wants of our being are not reached by them at all; whereas the "water" that Christ gives--spiritual life--is struck out of the very depths of our being, making the soul not a cistern, for holding water poured into it from without, but a fountain (the word had been better so rendered, to distinguish it from the word rendered "well" in Joh 4:11), springing, gushing, bubbling up and flowing forth within us, ever fresh, ever living. The indwelling of the Holy Ghost as the Spirit of Christ is the secret of this life with all its enduring energies and satisfactions, as is expressly said (Joh 7:37-39). "Never thirsting," then, means simply that such souls have the supplies at home. into everlasting life--carrying the thoughts up from the eternal freshness and vitality of these waters to the great ocean in which they have their confluence. "Thither may I arrive!" [BENGEL].

— Jamieson-Fausset-Brown Commentary (public domain)