Generally, in the Scriptures, streams, fountains, rivers, are used as emblematic of the abundant fullness and richness of the mercies which God has provided to supply the spiritual necessities of men. The idea here is, therefore, that they should partake abundantly of the mercies of salvation; that it was free, overflowing, and refreshing - like waters to weary pilgrims in the desert; and that their partaking of it would be with joy. It would fill the soul with happiness; as the discovery of an abundant fountain, or a well in the desert, fills the thirsty pilgrim with rejoicing.