In this graduate thesis, we explored the beatitude of the "pure in heart" in Matthew's Gospel. The goal was to show why purity of heart is one of Jesus' demands on his disciples to attain the Kingdom of God, using the method of synthesis and deduction. The thesis is divided into three chapters. Throughout all three chapters, an attempt is made to give a theological representation of the importance and very meaning of the beatitude of the "pure in heart". Matthew wrote his Gospel for his community, the converted Jews to Christianity, who accepted Jesus Christ as the Messiah, and in whom the fulfillment of God's will was accomplished. Christ fulfilled the law of Moses and thus brought to men a new law of love according to which they must act in order to attain the Kingdom of God, for which it is necessary to have a pure heart. Namely, Matthew does not want his community to only externally observe the Law, but asks them to carry it out, thus directing them to their interior. That is why he emphasizes the purity of heart, which he brings to us in the beatitudes with which the Sermon on the Mount begins, as a new attitude towards the Law. If the heart is corrupt, so are its relationships with God, others, and itself corrupt. Jesus Christ brings the beatitudes as a congratulation for the realization of the Kingdom of God. He showed us with his life an example of complete purity of heart and therefore by following him in everyday life, like him we will be able to see God as he promised us already here on earth by the time we see him as he is. Saints such as Augustine, Francis of Assisi, Mother Teresa, and John Paul II. they are witnesses to the importance of the beatitude of the "pure in heart" who, by their example of life, have proved the realization of that beatitude.