Organon of Medicine

§ 18 Sixth Edition

From this indubitable truth, that besides the totality of the symptoms with consideration of the accompanying modalities (§ 5) nothing can by any means be discovered in disease wherewith they could express their need of aid, it follows undeniably that the sum of all the symptoms and conditions in each individual case of disease must be the sole indication, the sole guide to direct us in the choice of a remedy.

Prasad Rasal
In this aphorism, Dr Samuel Hahnemann want to explain the importance of the language of the disease for the purpose of finding out the similimum. He has already explained it while explaining the Qualities of Homoeopathic Physician in the Aphorism no.3 that he should have the" knowledge of Disease, indication". So, in one sentence, he has explained the need of having the knowledge of the diseases from pathological point of view in order to understand the disease pathology & pathogenesis along with the understanding of its prognosis but not from prescribing point of view. He used the next word i.e. indications which is important for prescribing point of view. Because, the disease get expressed thro' signs & symptoms along with the state of the individual expressed thro' sensations, modalities & concomitants. These modalities gives the characteristic appearance to the sign & symptom which is very useful to find out the Similimum. For e.g. Asthmatic breathlessness agg. at 12 midnight, better by drinking sips of warm water directly gives hint to us regarding the Ars alb. If it's only Asthma as a diagnosis, we cannot find out the medicine on the basis of pathology.
That's why he says ... from this indubitable truth, that besides the totality of the symptoms with consideration of the accompanying modalities (§ 5) nothing can by any means be discovered in disease wherewith they could express their need of aid, it follows undeniably that the sum of all the symptoms and conditions in each individual case of disease must be the sole indication, the sole guide to direct us in the choice of a remedy.