The number 7 represents spiritual perfection, divine completion, and/or God's great works (I would say kingship as well, as we're talking about King David). That's why it's no surprise that 'El' (hebrew word for God) equals 17, 'God' equals 17, and 'Lord' equals 59, which again is the 17th prime number, and don't forget that 17 is the 7th prime number. Going back to King David, who is credited with writing many of the 'Psalms' and portions of the books of 'Samuel', note that 'Psalms' and 'Samuel' both equal 17 (of course, a young King David was anointed by the prophet 'Samuel'). Speaking of books in the bible, the phrases 'Holy Bible' and 'The Bible' both equal 153, which is the 17th triangular number.
For more significance related to this topic and these numbers (specifically the number 7), according to the bible, it took God 7 days to create the universe, and of course, there are 7 days in a week. There were 7 kings of 'Revelation' described in the 17th chapter of the book, there were also 7 churches of 'Revelation', and 'Revelation' equals 49 and 59, 49 is 7 squared, and 59 is the 17th prime number (AGAIN 17 is the 7th prime #). There are 7 main chakras in the human body, and the 7th is the crown chakra, which is why it's fair to say that the number 7 represents kingship.