Continued from here….
Christ still more urgently sets forth in His precepts with yet greater power of His rebuke.
“When ye stand praying,” says He, “forgive if ye have aught against any, that your Father which is in heaven may forgive you your trespasses.
“But if ye do not forgive, neither will your Father which is in heaven forgive you your trespasses” (Mark 11:25).
There remains no ground of excuse in the day of judgment, when you will be judged according to your own sentence; and whatever you have done, that you also will suffer.
For God commands us to be peacemakers, and in agreement, and of one mind in His house.
And such as He makes us by a second birth, such He wishes us when new-born to continue, that we who have begun to be sons of God may abide in God’s peace, and that, having one spirit, we should also have one heart and one 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 a peace-maker.
Our peace and brotherly agreement is the greater sacrifice to God—and a people united in one in the unity of the Father, and of the Son, and of the Holy Spirit.
For even in the sacrifices which Abel and Cain first offered, God looked not at their gifts, but at their hearts, so that he was acceptable in his gift who was acceptable in his heart.
Abel, peaceable and righteous in sacrificing in innocence to God, taught others also, when they bring their gift to the altar, thus to come with the fear of God, with a simple heart, with the law of righteousness, with the peace of concord.
With reason did he [Abel], who was such in respect of God’s sacrifice, become subsequently himself a sacrifice to God; so that he who first set forth martyrdom, and initiated the Lord’s passion by the glory of his blood, had both the Lord’s righteousness and His peace.
Finally, such as are crowned by the Lord, such will be avenged with the Lord in the day of judgment; but the quarrelsome and disunited, and he who has not peace with his brethren, in accordance with what the blessed apostle and the Holy Scripture testifies…, shall not be able to escape the crime of fraternal dissension.
Cyprian of Carthage (d.258): On The Lord’s Prayer, 23-24.