In "Biblical Perspective" I.C. Holland writes:
Watchmen were on duty in the Temple. Psalm 134 speaks to the “servants of the LORD, which by night stand in the house of the LORD.” For the safety of the people who dwelt in walled cities, watchmen kept their courses day and night. To Ezekiel, God said, “Son of man, I have set thee a watchman unto the house of Israel; therefore thou shalt hear the word at my mouth, and warn them from me” (33:7). The prophets of old were “God's remembrancers,” as are preachers and pastors of the Church age. It is their solemn business “to call to God's remembrance the needs and claims of His people, and the obligations of His covenant promises” (Pulpit Comm.). This we can understand to be importunate and intercessory prayer, the duty of all Christians. Paul taught us to pray without ceasing. In our prayers, we Christians are allowed to remind God of our faith in His covenant promises.
Source: Building Christian Relationships: Adult Teacher's Insights, page 12.