A key indicates control or authority; therefore, having the Key of David would give one control of David’s domain, i.e., Jerusalem, the City of David, and the kingdom of Israel.
Revelation 3:7 - “And to the angel of the church in Philadelphia write: ‘The words of the holy one, the true one, who has the key of David, who opens and no one will shut, who shuts and no one opens."
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