If I were looking for a good illustration from the Bible of what it means to be "poor in spirit" I would point you to the story of the Prodigal Son.
This foolish young lad bought into the notion that being rich in material possessions was the essence of happiness. So, he coaxed his father into letting him have his inheritance in advance and he took the money and ran as fast and as far as he could from the rules and restraints of home to a place where the pleasures of self-indulgence would be his boundless!
But he ran out of loot before he ran out of lust and when he did, his party time friends decided it was time to depart! Suddenly his quest for happiness left him humiliated, hopeless, and hungry.
Finding himself in an urgent need for lunch money, he took the only job he could find feeding pigs in a pig sty. Here is a young man who was destined to own his father's farm now feeding hogs for a farmer far less compassionate than his father.
His hunger didn't stop before the paycheck started and the foolish lad found himself longing for the slop he was he was giving the swine. Surrounded by hogs and knee deep in mud and slop he began to think of home. His mistreatment at the hand of this farmer refreshed his recollections of how well his father had treated those who fed the pigs back home.
Showing sudden signs of common sense, the son reasoned that if he was going to slop hogs he may as well try to hire on with his dad. Without giving two weeks notice he waded through the mud, around the pigs and over the fence to return to his father with the little bit of strength he had remaining. Luke 15 records the reunion that happened when he met his father on the dusty road home:
“The son said to him, ‘Father, I have sinned against heaven and against you. I am no longer worthy to be called your son.’ “But the father said to his servants, ‘Quick! Bring the best robe and put it on him. Put a ring on his finger and sandals on his feet. Bring the fattened calf and kill it. Let’s have a feast and celebrate. For this son of mine was dead and is alive again; he was lost and is found.’ So they began to celebrate." Luke 15:21-24
What is particularly noteworthy is the spirit of the son's plea to his father. Several key phrases give indication of his "poorness of spirit":
1) "Father, I have sinned against heaven and against you....."
2) "I am no longer to be called your son...."
He left as a son but was returning in hopes of becoming a servant.
This is where it gets good!
We he came home properly poor, that is when he became prosperous!
His father lavished on him full privileges of a highly favored son! The robe of righteousness, the signet ring of authority and the sandals signifying sonship! He finally found the happiness he had been looking for but it wasn't in the way he had expected.
What a vivid illustration of what Jesus meant when He said, "Blessed are the poor in spirit....."!
Being "poor in spirit" is not just about humility. Humility assumes you had something to be proud of. Being poor in spirit is about depravity, confronting your absolute spiritual depravity and then confessing it to your Father. That is your one chance at happiness!