One of this introduction's central purposes is to establish the meanings of the key terms:
وَهِيَ هَاهُنَا لِبَيَانِ مَعْنَى الْفَصَاحَةِ وَالْبَلَاغَةِ
Here the introduction explains the meaning of fasaha and balagha.
Fasaha concerns freedom from specified defects and the intelligibility and fluency of words and speech. Balagha concerns appropriateness to circumstances alongside the requisite eloquence.
These are preliminary orientations, not substitutes for the formal definitions and detailed classifications in the following section.