Adam Clarke on John 4:14

Springing up into everlasting life - On this account he can never thirst: - for how can he lack water who has in himself a living, eternal spring? By this water our Lord means also his doctrine, explaining and promising the gifts and graces of the Holy Ghost, which proceed from Jesus Christ their fountain, dwelling in a believing heart. There is no eternal life without the Spirit; no Spirit without Christ; and no Christ to give the Spirit, without dwelling in the heart: this his whole doctrine proclaims.