6 I have set watchmen upon thy walls, O Jerusalem, which shall never hold their peace day nor night: ye that make mention of the Lord, keep not silence,
7 And give Him no rest, till He establish, and till He make Jerusalem a praise in the earth.
Watchmen on the Walls: The idea here is that God’s prophets and ministers were like the watchmen who could not hold their peace or give Him rest day or night until Prophecy was completely fulfilled in the full restoration of Jerusalem and Israel in their land.
Since cities were first built, walls have been built around them to protect them from invasion; the watchmen had the duty of warning the citizens if an attack was coming. The watchmen in this passage are not there to warn of attack, but to encourage the people and to continually pray to God for the complete restoration of Israel and Jerusalem.