King David was far from faultless. One thing that made him great in the eyes of G-d was applying Torah principles to effect change in his life. Malchut is said to have no attributes of its own but is the receptacle for all the others that came before it. It’s about taking that which G-d has given us and utilizing it to bring tikkun (repair) to our lives and the world – “sh arpening your skills” on a regular basis.
Though we consider ourselves as being in the ‘physical world,’ Torah says we simultaneously exist in four worlds. These have a parallel to our physical, emotional, intellectual and spiritual selves. The Kingdom may be “within us,” but only when a king humbly works to improve himself through Torah/the middot at all levels, is he able to rule properly.
“In relating to the first nine Sefirot, (in the full structure of ten) we are outside observers – admiring G-d’s handiwork objectively. We may be impressed but somehow it never quite becomes an overwhelming experience. It is only when we hear the voice of G-d echoing from within us – which is malchut – that we are truly transformed.”
– ‘Physics God and the End of the World,’ Dennis A. Wright, p. 149
“Malchut is the goal that G-d had in mind when He created the world. All of the other sefirot are only the means to see malchut emerge.”
(See “Malchut: The Kingdom Within” at http://www.aish.com/sp/k/48971776.html )