The reading of the Diamond Sutra (金剛經) is oftentimes a frustrating experience for intellectuals or students of (western) philosophy (unfortunately me being one!). Here the Buddha negates everything, and if YOU negate anything, the Buddha will negate your negation. And in anticipation of the mentally alert, the Buddha eventually negates his own teaching! (for the benefit of students who like to argue, the Buddha also negates "anything goes"!)
A student of philosophy will wonder: does the Buddha teach anything in the Diamond Sutra?
The clue to the understanding the Diamond Sutra is the concept: Take it up and put it down.
The Buddha's audience in the Diamond Sutra consisted of celebrated monks who for years had perfected, to various levels, the practice of discipline (戒), meditation (定) and wisdom (慧). The Buddha, in the Diamond Sutra addressed this specific audience with the ultimate wisdom: the putting down of everything. The putting down of everything is not nothing. No matter what level of achievement in one's Buddhist practice, a Buddhist's ultimate enlightenment is to put down everything, including his pursue of morality and spirituality - not that he doesn't do it any more, but that he should continue to do, continue to improve, but no longer burdened by it (like "Am I doing it better than other?", "What level of enlightenment I'm at?", "I'm proud that I've attain this level", "I'm accepting my karma to suffer in this life, and I continue to do good things irrespective of how difficult they are"....). I mean, as if it is the most natural thing to do - as the Buddha said in chapter 2 "This is how to place one's heart 應如是住".
In Chinese Zen Buddhism, there is a saying, "Put down your killing sword and you become a Buddha" (放下屠刀，立地成佛). When a killer got a sudden enlightenment that sparing the life of the person (whom the killer said must die, for various reason) is a most natural thing to do (that first of all presupposes the [sudden] possession of compassion and [sudden] appreciation of morality in general), he can instantly become a changed person, in the sense that from this moment onwards he can (i.e. having the possibility) keep this enlightened state for the rest of his life! But of course, if this killer than decides to become a monk, he still has a lot to learn, yet he is enlightened.
In the Platform Sutra (六祖檀經), when Hui Neng heard the recitation of the Diamond Sutra (or one of its definitive verses), he became enlightened (in the sense of the Diamond Sutra of pick it up and put it down) but he was not yet a monk. He decided to become a monk and lead a monastic life. So after taking care of his mother financially, he went to the Fifth Patriarch's Monastery and learned how to lead a monastic life, which include the practice of Discipline (戒) and the practice of deep meditation that his Master ultimate taught him in private.
As for the modern man, he should understand that the practice of morality is the foundation to any high-level/ultimate enlightenment. The Buddha assured him, in the Diamond Sutra, irrespective of his level of morality achievement, he can get instantaneous ultimate enlightenment. And after his ultimate enlightenment (assuming that he can keep it!), he will not be burdened again in his path of further improvement.
As far as my humble understand goes, one doesn't need to be a Buddhist to learn and be benefited from this path of ultimate enlightenment as taught in the Diamond Sutra. And I rest my case.