He said he knew of three different ways to take it. The first is to go to a happy young soul who is joyous and praising God and say with a wagging finger, "blessed are those who mourn, young lady!" It would seem quite confusing and foreign.
Another way is to go to some bitter person whose family is all gone and who's been in prison being tortured their whole life. If you say, "blessed are those who mourn" to them, it will seem to be almost belittling or mocking their situation.
Boreham says that those who Jesus says are blessed are those who have know both joy and loss--when the calm has come afterward. "The eyes, cleansed by weeping, have obtained a clearer vision of life's profound mystery and beneficent discipline. The subject of this third picture knows the secret of the mourner's blessedness."