And it shall be in that day, that living waters shall go out from Jerusalem; half of them toward the former sea, and half of them toward the hinder sea: in summer and in winter shall it be. Living waters shall go out - There shall be a wide diffusion of Divine knowledge, and of the plan of human salvation, which shall go out by apostles and preachers, first from Jerusalem, then to Syria, Asia Minor, Greece, Italy, the isles of the sea, Britain, etc.
The former sea, and - the hinder sea - The Dead Sea and the Mediterranean; see on Joel 2:20 (note). These are metaphors.
In summer - In time of drought; or in the countries where there was no knowledge of God, there shall these waters flow. The stream shall never cease; it shall run in summer as well as winter. These are living waters - perennial, incessant, and waters that shall preserve life. See John 7:37.