Rightly is this blessedness promised to purity of heart. For the brightness of the true light will not be able to be seen by the unclean sight: and that which will be happiness to minds that are bright and clean, will be a punishment to those that are stained. Therefore, let the mists of earth’s vanities be shunned, and your inward eyes purged from all the filth of wickedness, that the sight may be free to feed on this great manifestation of God.
For to the attainment of this we understand what follows to lead. “Blessed are the peacemakers, for they shall be called sons of God” (Mt 5:9). This blessedness, beloved, belongs not to any and every kind of agreement and harmony, but to that of which the Apostle speaks: “We have peace with God” (Rom 5:1); as well as the Prophet David: “Great peace have those who love Thy law; nothing can make them stumble” (Ps 119:165).
This peace even the closest ties of friendship and exact likeness of mind do not really gain, if they do not agree with God’s will. Similarity of bad desires, leagues in crimes, associations of vice, cannot merit this peace. The love of the world does not consort with the love of God, nor does he enter the alliance of the sons of God who will not separate himself from the children of this generation. Whereas they whose minds are always with God, “eager to maintain the unity of the Spirit in the bond of peace” (Eph 4:3), never dissent from the eternal law, uttering that prayer of faith, “Thy will be done, on earth as it is in Heaven” (Mt 6:10).
These are the peacemakers, these are thoroughly of one mind, and fully harmonious, and are to be called “sons of God and coheirs with Christ” (cf. Rom 8:17), because on account of their love of God and neighbor, they shall suffer no calamities, and be in fear of no offence, but when all the strife of trial has ended, shall rest in God’s most perfect peace, through Our Lord, who, with the Father and the Holy Spirit, lives and reigns for ever and ever. Amen.
Source: St. Leo the Great. On the Beatitudes. Sermon XCV, 8-9