"Agree with thine adversary quickly while thou art in the way with him, lest at any time he shall get thee, and thou shalt be cast into prison. Verily, verily, I say unto thee, thou shalt by no means come out thence until thou hast paid the uttermost senine. And while ye are in prison can ye pay even one senine? Verily, verily, I say unto you, Nay."
This notion of agreeing with your adversaries is difficult for most people. It requires you to submit to what is sometimes unjust demands. He is saying to submit anyway. Do not rebel against the adversaries in life, but accommodate them.
Give to the unjust what they demand, so that they may see your good works and understand there is a higher way. Without your example, they cannot understand.
Retaliation continues the cycles. Someone eventually needs to lay down their just claim for retribution and simply take the injury without returning anything in return. This was what Christ did. He took everyone's injuries and returned only forgiveness.
Now He asks for His followers to do some of the same. The failure to tolerate injustice can spiral into continuing the conflict, until there is prison. The prison to fear is not one made by men. But if you are cast into that prison then you cannot come out until you have paid the highest price. (D&C 76: 84-85, 105-106.) It is better to repent because this payment made even God, the greatest of all, to tremble with pain and shrink from the burden. (D&C 19: 15-18.)
It is not possible to pay the price while in prison. The price must be paid by a person while in the flesh. (Luke 16: 22-26.) Any who are consigned to prison dwell in darkness, awaiting deliverance from Him whom they rejected while in the flesh. (D&C 138: 20-22.) They become dependent upon others working to pay the debt on their behalf. (D&C 138: 33.)
The sermon delivered by Christ is the foundation of how man ought to relate to fellow-man. It is the pattern on which it becomes possible to dwell in peace with one another. It is the groundwork for Zion.
We need to look at this sermon as the guideline for changing our internal lives, so we may become a fit and proper resident with others who are Saints. Even Saints will give inadvertent offenses. Even Saints will disappoint one another from time to time. To become "one" in the sense required for redeeming a people and restoring them again to Zion is beyond any person's reach if they cannot internalize this sermon.
The purpose of this sermon is not to equip you to judge others. It has no use for that. It is designed to change you. You need to become something different, something higher, something more holy. That will require you to reexamine your heart, your motivations, and your thoughts. It will require you to take offenses and deliberately lay them down without retaliation. When you do, you become someone who can live in peace with others. Living in peace with others is the rudimentary beginning of Zion. It will not culminate in a City set on the hilltop until there is a population worthy of dwelling in the high places, in peace, without poor among them. (Moses 7: 17-18.)
Christ's sermon is not merely a description of what kind of person He is. It is a description of what kind of person will qualify to live with Him. (Luke 9: 23.)