"Guardian", "Watchman" is the symbol of God's Prophet, who is "set up", encouraged, raised up by God by the knowledge of His Will to warn, guard the nations against the spiritual danger of perversions, violations of God's Will and their consequences.
"Watchmen" is also an image of the spiritual mission of all the Righteous - to be guardians of the true knowledge and fulfillment of God's Will.
Negative Meaning.
"Guardian", "Guardian" is a symbol of the religious leaders, shepherds of the people, who, knowing the Will of God, themselves distort and violate it, do not care to acquire, preserve the true understanding of the sayings of the Prophets, Christ and Apostles, do not fulfill their spiritual mission - do not warn people of the tragic consequences of distortions, violations of the Will of God.