The art of being poor in spirit is to distinguish between use and ownership. A person who owns something or regards himself as an owner, believes he has the sole right to determine how that thing is used. He may use it himself or authorize another person to use it. But this sense of ownership is a terrible snare, because it prevents a person’s soul from marching onward toward God. The person who wishes to move towards God must free himself from all sense of ownership. He must regard all things as loans from God, even the things that he himself owns. A loan is to be used for a period, and then paid back. This is precisely how we should regard our houses and fields, clothes and furniture; they are loans which God grants us for our short span on earth, to be repaid at the moment of death. To be poor in spirit does not mean to be destitute, lacking in even the basic comforts and necessities. It means to regard nothing as your own, and everything you have as a temporary loan.
St. John Chrysostom