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."

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit myeveningdevotional.substack.com/subscribe