PEACEMAKER (εἰρηνοποιός, G1648, the one who makes peace or reconciles parties who are in conflict). “Blessed are the peacemakers, for they shall be called sons of God” (Matt 5:9). The believer is to function as such, finding his example in Christ.

Christ reconciled man to God in offering Himself as a sacrifice to satisfy God’s divine justice (Rom 5:1; Col 1:20; cf. Eph 2:14-17). Through the proclamation of the Gospel men are reconciled to God and act as peacemakers (2 Cor 5:18, 19).

International Standard Bible Encyclopedia (1915)

pes’-mak-er: Occurs only in the plural (Mt 5:9, "Blessed are the peacemakers (eirenopoioi): for they shall be called sons of God" (who is "the God of peace")). We have also what seems to be a reflection of this saying in Jas 3:18, "The fruit of righteousness is sown in peace for (the Revised Version margin "by") them that make peace" (tois poiousin eirenen). In classical Greek a "peacemaker" was an ambassador sent to treat of peace. The word in Mt 5:9 would, perhaps, be better rendered "peace-workers," implying not merely making peace between those who are at variance, but working peace as that which is the will of the God of peace for men.