A branch is produced by the root. While the branch may come to fulfill an entirely different purpose than the root, it is, nonetheless, indebted to it. It also cannot survive without the root. So, in perhaps a circuitous way, the branch is tied to the root, figuratively and literally.
Branches do not thrive, let alone survive, by severing themselves. In fact, the primary way a branch can survive (should it become severed) is if it is grafted on to another plant which has a root. The branch’s well-being is tethered to the root.
Such is the way to explain ‘asl and far’ (فرع/أصل), in the study of Usul al-Fiqh, as well as the application and implementation of sacred knowledge and overall success as a Muslim. Far too many of us today seek success as branches, heedless of our attachment to roots.
Usul al-Fiqh (the foundation of understanding) constitutes two definitions, made up of two single parts:  ‘asl, (lit., “root”), which something — besides itself — builds off of and far’ (lit., “branch”), which itself is built upon something else.  Fiqh (lit., “understanding”), is knowledge of sacred rulings, the path to which is known as ijtihad (independent legal reasoning, lit., “to push oneself in striving”.
أصول الفقه مؤلف من جزأين مفردين: فالأصل – ما يبنى عليه غيره والفرع ما يبنى على غيره والفقه – معرفة الأحكام الشرعية التي طريقها الاجتهاد
A short excerpt taken from al-Juwayni’s al-Waraqat.