“If you bring your gift to the altar, and there recall that your brother has anything against you…go first and be reconciled with your brother”
"The measure with which you measure shall be measured out to you" (Mt 7:2). And the servant who, after having had all his debt forgiven him by his master, would not forgive his fellow-servant, is confined to prison. Because he was unwilling to forgive his fellow-servant, he lost the forgiveness which had been granted him by the Lord (Mt 18:23f). And these things Christ sets forth still more strongly in his precepts by the greater force of his censure. He says: "When you stand praying, forgive anyone against whom you have a grievance, so that your heavenly Father may turn forgive you your transgressions. But if you do not forgive, neither will your heavenly Father forgive your transgressions" (Mk 11:25)...
For God commands us to be peacemakers and of one heart and of one mind in his house. And such as he has made us by a second birth, so by a second birth he wishes to preserve us , that we who are the children of God may abide in the peace of God, and that we who have one spirit may have one heart and mind. Thus God does not receive the sacrifice of a person who is in disagreement but commands him to go back from the altar and first be reconciled to his brother, that so God also may be appeased by the prayers of the peacemaker. The greater sacrifice to God is our peace and fraternal concord and a people united in the unity of the Father and of the Son and of the Holy Spirit.