This is a current reflection:
[T]he truth that constitutes the church means that the lies of the world cannot help but be exposed by the way Christians are required to live. — Hauerwas, Stanley (2007-01-01). Matthew (Brazos Theological Commentary on the Bible) (p. 71). Baker Publishing Group. Kindle Edition.
The heart of the Sermon on the Mount is the conviction that the cross and not the sword, suffering and not brute power determines the meaning of history. The key to the obedience of God’s people is not their effectiveness but their patience. The triumph of the right is assured not by the might that comes to the aid of the right, which is of course the justification of the use of violence and other kinds of power in every human conflict. The triumph of the right, although it is assured, is sure because of the power of the resurrection and not because of any calculation of causes and effects, nor because of the inherently greater strength of the good guys. The relationship between the obedience of God’s people and the triumph of God’s cause is not a relationship between cause and effect but one of cross and resurrection. (Yoder 1994b, 232) — quoted in Hauerwas, Stanley (2007-01-01). Matthew (Brazos Theological Commentary on the Bible) (p. 72). Baker Publishing Group. Kindle Edition.
It is said that living the Sermon on the Mount is plain impossible. I am not sure that that is actually the case but I will gladly note that it is not likely that anyone will actually do so cleanly. That is to say: those who would dare to be guided by the Sermon on the Mount remain sinners. As such any attempt is likely to lead to many failures. Jesus and Matthew knew this. One could look at chapter 18 to figure out that failure was an option since it is obviously anticipated and a remedy is being proposed.
Some realities: Turning the other cheek will most likely lead to being struck on the other cheek as well. My suspicion, having watched enough martial arts, is that the one turning the other cheek will be unconscious before the attacker tires of striking, unless they are in horrible physical shape.
Maybe this is not to be taken literally. Maybe, this is a matter of having to tell the truth (5:37) repeatedly to a world that does not wish to hear it and suffering repeatedly the wrath of that world.
No one wants to be told the truth about themselves. We want to be flattered. We want to hear that we are “OK” and “them,” well, “them” is reprobate in some way. No one even wants to hear: “We are not OK, they are not OK, but that is OK.” If one says anything like it, the response would be somehow that: “Yes, we are all sinners but we are OKer then them, right?”
There seems to be no really valuable “us” vs. “them” divide that one can make if Jesus words are believed. Morning comes and the sun warms the windows of the worst of the “them” as much as the best of the “ours.” “Their” lives are quite ordinary if one was to investigate the matter. “They” do not kick puppies ever day and “they” don’t punch old ladies. “Their” crops grow and “their” children grow up. “Their” family loves one another. (5:45-46)
Sure, we can insist that God, please, judge “them” by the actions that offend us and according to “their” sins and visit retribution upon them. We are available to help meting that out. Grant the chance to serve you thus, dear Lord.
And the strikes to the cheek are equally likely to come, not from the “them,” but from other of the “us” who would be vexed to hear that we have no excuse, whoever we are, when we judge; for in passing judgment upon “them” we condemn ourself. (Rom 2:1)
It was Jesus himself who announced that he had come to bring not necessarily peace but the sword. (Matt 10:34) Exposing the sin of the world has that result. It is one reason that the world decided to crucify him.
Those who would be grown ups (5:48) — and Jesus hopes his church will be the grown ups about the sin of the world — are those who have come to terms with the reality that the facts and forces are what they are and one one must name them. It is dirty work but someone has to do it. There will not be anything that resembles community or church unless someone takes up the task, just as there is no such thing as salvation unless Christ takes up the task to call sin what it is so that it can be forgiven.
To live the Sermon on the Mount is an exercise in growing up and facing facts about ourselves, of repenting and living truth. Merely doing that, will likely bring the slaps of offended ones who would like to live their lies. The really question is: “Are there ANY grownups around us today?”