هِيَ لِلدِّينِ قَوَاعِدُ وَأُصُولٌ
These are rules and foundations for matters of religion.
A faṣl is an organizational section. A qāʿidah is a general principle applicable to many questions. An aṣl is a fundamental basis or source. These terms are related, but they do not always perform the same intellectual function.
Example:
Affirming divine perfection while denying imperfection is a foundational theological principle.
It may inform several specific questions about attributes.
Those questions may be arranged under a dedicated section.
Proper organization makes the relationship among principle, argument and result easier to understand.