The publican's is the language of the poor in spirit. We do not belong anywhere except alongside the publican, crying out with downcast eyes, "God be merciful to me a sinner!" John Calvin, the sixteenth-century theologian whose teachings form the basis of Reformed Protestantism, wrote, "He only who is reduced to nothing in himself, and relies on the mercy of God is poor in spirit" (Commentary on a Harmony of the Evangelists, Matthew, Mark and Luke, p. 261).
Notice how Jesus brought out that the underlying attitude of the Pharisee was reliance in self. He boasted before God of all his "excellent" qualities and works, things he evidently thought would earn him God's respect. His vanity about these things then motivated him to regard others as less than himself. So we see that self-exaltation is the opposite of poor in spirit.
Poor in spirit is contrary to that haughty, self-assertive, and self-sufficient disposition that the world so much admires and praises. It is the reverse of an independent and defiant attitude that refuses to bow to God—that determines to brave things out against His will like Pharaoh, who said, "Who is the Lord, that I should obey His voice . . .?" (Exodus 5:2). A person who is poor in spirit realizes that he is nothing, has nothing, can do nothing—and needs everything, as Jesus said in John 15:5, "Without Me you can do nothing."
In his commentary, The Sermon on the Mount, Emmett Fox provides a practical description of what "poor in spirit" means:
To be poor in spirit means to have emptied yourself of all desire to exercise personal self-will, and, what is just as important, to have renounced all preconceived opinions in the whole-hearted search for God. It means to be willing to set aside your present habits of thought, your present views and prejudices, your present way of life if necessary; to jettison, in fact, anything and everything that can stand in the way of your finding God. (p. 22)
Poverty of spirit blooms as God reveals Himself to us and we become aware of His incredible holiness and towering mercy in even calling us to be forgiven and invited to be in His Family—to be like Him! This understanding awakens us to the painful discovery that all our righteousness truly is like filthy rags by comparison (Isaiah 64:6); our best performances are unacceptable. It brings us down to the dust before God. This realization corresponds to the Prodigal Son's experience in Luke 15:14 when "he began to be in want." Soon thereafter, Jesus says, he "came to himself" (verse 17), beginning the humbling journey back to his father, repentance, and acceptance.