Here is a quote from
Abhidharmaye Mūlika Karuṇu
(Basic facts of Abhidhamma)
By
Rerukāne Candavimala Mahā thero
Translated
By
D.J. Percy Silva
Sutta Dhamma are like prescriptions written by a physician after examining various patients. Abhidhamma Piṭaka is like the medical knowledge possessed by the physician. One cannot become knowledgeable in Dhamma by learning the Sutta Piṭaka which is like a lot of prescriptions; like it is not possible to become a physician by reading prescriptions rather than methodically studying medical science. Cannot become learned in Dhamma or a good Dhamma speaker. The Dhamma knowledge of the person who does not know Abhidhamma is confused. Dhamma discourses are also not pure. The confusion and faults in it can be seen only by those who know Abhidhamma and not by others. Therefore, others praise such confusing discourses. The deliverer who does not know the status of the discourses too is pleased. Sometimes feels proud of oneself. Such wrong idea remains until Abhidhamma is learnt. The commentary on Abhidhamma named, ‘Atthasālini’ shows the Dhamma discourses by one not learned in Abhidhamma as follows.
“Ābhidhammika bhikkhu yeva kira dhammakathikā nāma, avasesā dhammaṁ kathentāpi na dhammakathikā. Kasmā? Te hi dhammaṁ kathentā kammantaraṁ vipākantaraṁ rūpārūpaparicchedaṁ dhammantaraṁ āloletvā kathenti. Ābhidhammikā pana dhammantaraṁ ālolenti. Tasmā Ābhidhammikā bhikkhu dhammaṁ kathetu vā mā vā26 pucchita kale pana kathessatī ti so yeva dhammā kathiko nāma hoti.”
“It is the bhikkhus learned in Abhidhamma that are Dhamma speakers. Although others deliver Dhamma, they are not Dhamma speakers. Why is it? They deliver Dhamma, confusing one kamma with another kamma, confusing one result with another result, confusing material with non-material and confusing one dhamma with another dhamma. Those learned in Abhidhamma do not confuse the Dhamma. Therefore, whether or not the Bhikkhu learned in Abhidhamma delivers Dhamma discourses, he definitely becomes a Dhamma speaker because he correctly explains matters when questioned by others.” Is its meaning. Facts being so, those who need to learn Buddhism should study the Abhidhamma Piṭaka.