Matthew 5:9 English Standard Version (ESV)
Blessed are the peacemakers, for they shall be called sons of God.
The seventh beatitude is the hardest of all to expound ("Blessed are the peacemakers: for they shall be called the children of God," Matthew 5:9). The difficulty lies in determining the precise significance and scope of the word peacemakers. The Lord Jesus does not say, "Blessed are the peace-lovers," or "Blessed are the peace-keepers," but "Blessed are the peacemakers." Now it is apparent on the surface that what we have here is something more excellent than that love of concord and harmony, that hatred of strife and turmoil, that is sometimes found in the natural man, because the peacemakers that are here in view shall be called the children of God.
This seventh Beatitude has to do more with conduct than character; however, of necessity, there must first be a peaceable spirit before there will be active efforts put forth to make peace. Let it be remembered that in this first section of the Sermon on the Mount, the Lord Jesus is defining the character of those who are subjects and citizens in His Kingdom. First, He describes them in terms of the initial experiences of those in whom a Divine work is wrought. The first four Beatitudes may be grouped together as setting forth the negative graces of their hearts. Christ’s subjects are not self-sufficient, but consciously poor in spirit. They are not self-satisfied, but mourning because of their spiritual state. They are not self-important, not lowly or meek. They are not self-righteous, but hungering and thirsting for the righteousness of Another. In the next three Beatitudes, the Lord names their positive graces. Having tasted of the mercy of God, they are merciful in their dealings with others. Having received from the Spirit a spiritual nature, their eye is single to behold the glory of God. Having entered into the peace that Christ made by the blood of His cross, they are now anxious to be used by Him in bringing others to the enjoyment of such peace.
The believer in Christ knows that there is no peace for the wicked. Therefore, he earnestly desires that they should acquaint themselves with God and be at peace (Job 22:21). Believers know that peace with God is only through our Lord Jesus Christ (Colossians 1:19, 20). For this reason we speak of Him to our fellow men as the Holy Spirit leads us to do so. Our feet are "shod with the preparation of the Gospel of peace" (Ephesians 6:15); thus, we are equipped to testify to others concerning the grace of God. Of us it is said, "How beautiful are the feet of them that preach the Gospel of peace, and bring glad tidings of good things!" (Romans 10:15). All such are pronounced blessed by our Lord. They cannot but be blessed. Next to the enjoyment of peace in our own souls must be our delight in bringing others also (by God’s grace) to enter into this peace. In its wider application, this word of Christ may also refer to that spirit in His followers that delights to pour oil upon the troubled waters, that aims to right wrongs, that seeks to restore kindly relations by dealing with and removing difficulties and by neutralizing and silencing bitterness.