Blessed are the peacemakers, for they shall be called sons of God. A peaceful person repays good for good, as far as in him lies, and wishes harm to no one. Someone else may be patient and repay no one evil for evil, being even able to bear with the one who hurts him. There is also the peacemaker: he is always ready to repay good for evil and to help the one who hurts him. The first is one of those little ones who is easily scandalized; for him it will not be easy to win salvation in this present evil age so full of stumbling blocks. The second possesses his soul in patience, as has been written. As for the third, he not only possesses his own soul, but wins many more. The first, as far as he is able, is in peace. The second keeps peace. The third makes peace. Appropriately therefore is he blessed with the name son, for he accomplishes the duty incumbent on the son: that once he has himself been acceptably reconciled, he in turn reconciles others to his Father. Now someone who serves well gains good standing for himself, and what better standing could there be in the father’s house than that of the son? For, ‘if sons, then heirs, heirs of God and fellow heirs with Christ.’ And so it is, as he himself has said, that where he is, there shall his servant be also.
Bernard of Clairvaux, Sermons on Conversion: On Conversion, A Sermon to Clerics, v 31 (CF 25, p. 68f)