I surely recommend the Diamond Sutra in Mahayana Buddhism. It has :
a)The non-duality of the Prajnaparamita
b)The amazingly superb way of constructing language to point to a core truth of the nature of all dharmas, things, we may say. This can only be carried out by some most brilliant monks somewhere in the last century before Christ and the first after in India, through their deepest understanding of the teaching, the truth shown by Buddha to generations of students and disciples. The prodigy in using language to expose/expound the meaning through meditative experience, learning, contemplating, and practicing Buddhist Way of Life and path to Enlightenment is nothing less than marvelous
1. Read it the first time after a few years of learning basic tenets, some other scriptures. Read and comprehend certain amount of philosophical discourses on Buddhism. Read the sutra thoroughly with comments, explanations from monks, nuns, teachers; think, and ponder hard on it. Let it stay with you for, say 3, 5 years with frequent pondering upon it.
2. Learn meditation, especially Vipassana meditation, practice for some years, then go back to the Diamond Sutra a second, third time to see how your exploration in understanding it has developed. Again stay with it.
3. At year 10, 12, 15 , read it again to see how far you can understand it, in comparison with other sutras and sastras in the Prajnaparamita, for example with the multi-depth Prajnaparamita Hridaya Sutra, the Complete Understanding Sutra (kinh Viên Giác)
4. Don’t rest assured you have understood it thoroughly just by understanding it through conceptual analysis and explication. Be sure to understand it through meditation and contemplation. Understand it like you were in the dark and suddenly see light and absorb that light instantly.
5. I believe, once you can truly understand why the monk authors (not necessarily Buddha) use only the examples on the characteristics of the self, (other) persons, (sentient) beings, “souls” and the example on the characteristics of Buddha’s ( body, face, hands, etc)[ Ed Conze: marks of Tathagata (=Buddha)] – but not anything else— to show the disciples not to trust/believe that’s the “real” Buddha, then you have comprehended the sutra really deeply. Behind that genius of a way of constructing idea through language is years and years of learning and practicing
Maybe you may want to know this : It took our poet genius, Nguyen Du, more than a thousand times to read this Diamond Sutra, and still there were places in that sutra he did not quite understand. So don’t rush yourself.
Let me be clear. In “once you can truly understand why the monk authors (not necessarily Buddha)…” in the article, what I mean is : The main essence of the Sutra, such as Suñña( the Void), non-duality, had been taught by Buddha to the monks, but the wordings, the constructive language of the Diamond Sutra were recorded or created by the Mahayana monks. We do not find the Diamond Sutra in 5 Nakàyas of Theravada Buddhism. Around 400 years after Buddha’s passing away, there were around 18 schools of Buddhism among Theravada and Mahayana Buddhists in India within that period of differentiation. Therefore, different recordings existed (i.e. texts, for example, on palm leaves), and so did differences in the languages of the texts.