Rev. 3:7 "And to the angel of the church in Philadelphia write, 'These things says He who is holy, He who is true, "He who has the key of David, He who opens and no one shuts, and shuts and no one opens".
Nobody goes anywhere or gains access to anything these days without keys - Keys for the house, car, work locker, desk, filing cabinet - everywhere you go you need keys. In todays computer age you need ID keys to LOGIN, and passwords to gain access to member sites or areas of privileged information. The key represents ownership of something or permission to use something. It also gives you permission to go somewhere or do something you otherwise would not be able to do. It can give you access to privileged information, answers to questions and insight to things otherwise hidden. Very useful things and essential to have. Not until we lose a key - and we find ourselves without access to something we have generally taken for granted - are we suddenly reminded of its importance. When our credit card is stolen, we suddenly have a fresh appreciation of the power we have lost, now in someone elses hands, which must be retrieved at all costs, with no small measure of urgency.
The Kingdom of God has keys, given to certain individuals to operate in the power of kingdom authority, and withheld from others whose use of them would be undeserving or inappropriate. King David in the Old Testament had one of these keys. His use of it and understanding of its importance we now associate with the key itself - we call it "David's key" or "The key of David." What was the key of David? A study of the man's life will help reveal the answer to this question.
He was firstly a man after God's own heart. That means whatever He did with whatever keys he got was not going to be about himself, there was a higher purpose beating in the heart of David.
He was a worshiper. He thought it was important enough to make sure it never stopped. He organised 24 hours continuous worship in the tabernacle, and wrote many of the psalms we still read today. "Ever praising thee" was definitely one of David's keys.
"Blessed are they that dwell in thy house: they will be still praising thee. Selah. Blessed is the man whose strength is in thee; in whose heart are the ways of them." Psalm 84:4,5