This article is mainly based on Paul Tillich's thought that explores the root of human reason comes from God. The author emphasizes that God's revelation does not conflict with human reason, but instead it leads human reason to seek God's revelation If the nature of human reason is rooted in God, why do reason and faith sometimes oppose to each other? Paul Tillich believes that the conflict between both lies in the finite nature of human being. Paul Tillich says that in the finiteness of human being, the anxiety of death will lead us tend to open to God, and God becomes our ultimate concern, with the courage to be, overcome our anxiety of death. In human alienation, Paul Tillich regards that Jesus Christ as the new being reveals to us, and become our ultimate concern to overcome our anxiety of meaninglessness of life. In the ambiguity of human life, Paul Tillich says that the Holy Spirit becomes our ultimate concern, and the power of the Spirit is within our spirit, to overcome our anxiety of moral condemnation, and finally guide us to reconcile with God.