مرجع البلاغة في الكلام
The basis on which balagha in discourse depends.
Here marjaʿ means the necessary basis or conditions on which attaining the quality depends. The discussion is not another definition of balagha; it identifies the knowledge and safeguards needed to realize it.
Keep two questions distinct:
1. What is baligh discourse? Fasih discourse conforming to the occasion.
2. What errors must one avoid and what discriminations must one learn to produce it? This is the concern of marjaʿ al-balagha.