William Burkitt on John 7:38

Here again Christ alludes to a Jewish custom; the Jews were wont at fountains to build great vessels of stone, and in the midst or belly of them to have pipes, through which the water passes. "Now, says Christ, Thus shall it be with every one that believeth on me; he shall be abundantly filled with the spirit of God, in all the sanctifying and saving graces of it." Christ and his Holy Spirit are a living fountain, whose waters never fail; they are not a water-brook, but a spring of waters: we shall never miss of the waters of life, if we seek unto and wait upon Christ for them. For if we believe on him out of our belly shall flow rivers of living waters, sufficient for ourselves, and wherewith to refresh others.