There is a popular belief—a conceit no doubt originated by the authors of the Commentaries themselves, and fostered by their disciples — that the interpretations and authority of the Commentaries are derived from pakiṇṇakadesanā—some obscure passages scattered here and there in the Suttas, known only to deep scholars. Another questionable idea deeply rooted in the Sāsana is that the Sutta-Piṭaka is simply the external teaching — the Buddha preaching to ordinary people in conventional language — implying that the Suttas are not as deep as later works compiled by the scholars themselves.
But the truth is that the Commentaries are derivative, not more ‘advanced’ than the Suttas. Very often they are inconclusive regarding the meaning of deep Suttas. They often give several possible — even mutually contradictory — interpretations. Sometimes, overlooking the direct meaning, they go off on a speculative tangent. The Commentaries are silent on some of the most profound Suttas, as if they don’t know what to say about them.
The Buddha foretold the dangers that would befall the Sāsana in the future:
“In times to come, monks will lose interest in those deep Suttas that deal with transcendental matters; they will not listen to those Suttas having to do with emptiness, suññatā. They will not think it worthwhile learning or pondering over the meanings of those Suttas.” — Āṇi Sutta (SN 20.7)
The Buddha is not foreseeing some remote future: it has already happened. According to the Manorathapūraṇī commentary on the Aṅguttara-nikāya, there was a debate early in the Sri Lankan Sāsana between the scholar-monks and the meditators. The unfortunate conclusion was that merely communicating the words of the Suttas and Commentaries would be sufficient for the continuity of the Sāsana, and that direct realization of the practice is not so important. So the basket (piṭaka) of the Buddha’s words came to be passed on from generation to generation in the dark — that is, without the corresponding realization.
Certainly much was lost as a result of that misguided decision. In practice, this has resulted in the monks emphasizing the derivative Commentaries more than the original words of the Buddha. This is visible in the division in Sri Lanka between the ritualistic temple monks—who generally wear bright, almost day-glo colored robes—and the meditators who prefer more sober vestments. Even among the meditators, most are university-educated, trained to value the words of the Suttas over the realities and realizations they are supposed to represent. Thus the monks chant the Parittā-Suttas with great facility, but cannot explain them in terms of Nibbāna or suññatā—to say nothing of realizing them for themselves. If you ask, they reply that they are ‘too busy’ managing their temples to devote much time to meditation.
Also there is a tendency in the Commentaries to elaborate on and obfuscate even perfectly clear words in the Suttas, simply as display of exegetical skill. This led to many unnecessarily complicated ideas; thus the deeper meanings of the Dhamma got obscured. Actually the depth of the Dhamma can be seen only through its simplicity and clarity, just as one can see the bottom of a lake only when the water is calm and pellucid. Unnecessary elaborations and interpretative complications led to obscuration of the clear meaning, and the unfortunate result today is that few followers of the Buddha’s path are becoming enlightened.