When poor is used this way, it means "to be destitute, without resources; weak, powerless; spiritually bankrupt." Being poor in spirit is the platform on which is built all of the other beautiful attitudes that please God and motivate Him to respond with spiritual and sometimes physical blessings. Our being poor in spirit is the recognition of our spiritual need that causes us to cry out to God for what He can and will supply. This same recognition also motivates us to think about God from the proper perspective, causing us to give Him praise and thanksgiving. It forces us to see Him for what He is and what He has and makes us long to be the same, just as the financially poor see and desire to be like the rich.
None of us can honestly say that we have never looked at those who are wealthier than we are and not desired to be like them, to be in their same position, to wear exquisite clothing, to live in large homes, to drive expensive cars, and to be recognized as a powerful influence in the community.
Being poor in spirit forces us to evaluate ourselves honestly against God. He is the exemplar of every good characteristic, the possessor of intelligence, wisdom, and power of such capacity that He can produce us and every other good and beautiful thing needed for a wonderful, abundant life. For us to have this point of view, God must prepare a great deal of groundwork because human nature with its pride is always standing in the way to guard its territory, its place in our thinking and decision-making.
John W. Ritenbaugh
New Covenant Priesthood (Part 3)