The poor in spirit represents a contrite heart that recognizes a need for God. We are impoverished spiritually due to sin. When we recognize that our relationship with God is broken, we seek the repair. When our spiritual eyes are opened, we see the answer is Christ and the cross. When we receive Him, it is our visa to enter the kingdom of heaven, given through His atoning work on the cross, and we enter the Kingdom of Heaven as His disciples. The journey of faith has begun from a humble contrite heart.
The beatitudes are about this Christian journey of faith. The first four beatitudes are about our inward journey of faith. Blessed are the poor in spirit, those who mourn, the meek, and those who hunger and thirst for righteousness. Each of these is about the development of our souls. Next Jesus looks at the outer person, the expression of our faith, our orientation to the world. Blessed are the merciful, the pure in heart, and the peacemakers. These beatitudes describe the Christian in engagement with the world as a result of the change in heart brought about by the first four beatitudes. How the world reacts, our former fellow citizens of the world, is presented in the next blessed statements. You are not championed for being merciful, pure in heart, or a peacemaker, but are persecuted, lied about and ridiculed. Our response is to rejoice and be glad for our reward is great in Heaven.
The beatitudes are a challenge for us to live a Christ centered life, transformed from a person ruled by self-will to one ruled by Christ. We don't make this journey alone but in fellowship with the Holy Spirit and within the Christian Community of the Church.