I was being a touch tricky, in order to introduce the idea slowly. I actually think that those beatitudes fit the teaching as well.
What Jesus is announcing is that the Kingdom of God is so valuable that whatever it costs you is worth it. He is not saying "Be merciful, and I will be merciful to you." He is saying "You can afford to be merciful no matter how much it costs you in this life. You can afford to act as mercifully as God. Has someone cheated you? Doesn't matter." He is not saying that it is a good thing that someone cheated you, or that you should seek being cheated, or that being cheated and enduring it is character building. Peacemakers are brought in not in our modern sense of arbitrators or wise rulers who can avert war and conflict - that is in fact a thorough misreading of the text, based on modern political ideas rather than Christian ones. Peacemakers in this sense are those who give up what is their just due, who swallow their pride and go along with bullies and evil men, not because that is a good thing to do, but because they can afford it. Now that the Kingdom of God has arrived even acceding to injustice, which seems so expensive and impossible to you now, should be counted as nothing.
This fits precisely with Peter's cry in Matthew 19 (Please cease racing through for the concepts - as I always do - and read these slowly)
27 Then Peter said to him, “We’ve given up everything to follow you. What will we get?”or with Paul's comment in Philippians 3
28 Jesus replied, “I assure you that when the world is made new and the Son of Man sits upon his glorious throne, you who have been my followers will also sit on twelve thrones, judging the twelve tribes of Israel. 29 And everyone who has given up houses or brothers or sisters or father or mother or children or property, for my sake, will receive a hundred times as much in return and will inherit eternal life.
7 I once thought these things were valuable, but now I consider them worthless because of what Christ has done. 8 Yes, everything else is worthless when compared with the infinite value of knowing Christ Jesus my Lord. For his sake I have discarded everything else, counting it all as garbage, so that I could gain Christ...Or with the parables of the kingdom of Matthew 13
44 “The kingdom of heaven is like treasure hidden in a field. When a man found it, he hid it again, and then in his joy went and sold all he had and bought that field.(And the rest of Matthew 13 as well, really.)
45 “Again, the kingdom of heaven is like a merchant looking for fine pearls. 46 When he found one of great value, he went away and sold everything he had and bought it.
Or the rich young ruler. The message is not "If you give up stuff, you will become a better person and start to learn about the Kingdom." The message is "You just don't get it. You are already poor in comparison to those who have embraced the Kingdom."
This is not a new teaching. But it has become obscured over the last few centuries, especially the 20th, and I believe especially in America. Certainly, this thought is integral to Boethius's Consolation. It was central to Catholic mystic and devotional thought - which even Catholics don't pay much attention to these days, never mind Protestants.* The modern idea - Hey! You Guys! You're supposed to be meek, and humble, and peacemakers, not rich bastards exploiting the poor - comes as a reaction to some people becoming wealthy. It's not really a spiritual idea, but a very earthly one, emerging, unsurprisingly, just as our general earthly lot improves.
I'm not saying a word against humility, or swallowing one's pride "just to keep peace," or enduring persecution. There are other places in scripture where these are offered as good ideas, and an object of obedience. I am saying they have little to do with the Beatitudes. And, less to do with the Gospel than we commonly think. What Jesus says the Gospel is contains a whole lot of "Nothing matters except believing in Me," and only secondarily "Believing in Me means doing x, y, and z."
Hey, I didn't say it. Jesus said it. Read for yourself.
*The dropoff is so severe that I suspect the percentage of Protestants who take sustenance from earlier Catholic devotion is not much lower than the percentage of Catholics. (See: Everyone Who Reads Richard Foster, for example).