Ibn Majah

Commentary:
(1)
Generally, from the term "fiqh" are understood matters such as prayer and fasting, and in transactions such as buying and selling, the lawful and unlawful, the obligatory and recommended, and their conditions, pillars, etiquettes, etc.
Beliefs (‘aqa’id) and morals (akhlaq) are considered separate sciences, but in the Noble Qur’an and the Prophetic hadiths, wherever words like "fiqh" and "tafaqquh" appear, these technical meanings are not intended; rather, what is meant there is the absolute knowledge and understanding of the religion, which includes, along with acts of worship and transactions, the rectification of the heart, purification of the soul (tazkiyah al-nafs), good character (akhlaq hasanah), and correct beliefs (aqa’id sahihah), etc.
Whoever attains knowledge of these matters can fulfill the rights of Allah, the rights of his own self, and, besides friends and relatives, the rights of the general Muslims and those in authority as well.
In this way, his life is molded in the pattern of the Qur’an and Sunnah, becoming a source of religious and worldly goodness and blessing, and he himself becomes a complete mercy for others. And this is that great good (khayr ‘azim) beyond which there is no greater good.

(2)
These blessings of religion and world can only be attained by the person who is acquainted with the Shari‘ah rulings regarding the aforementioned matters. Therefore, from this, the importance and necessity of learning religious knowledge becomes clear.

(3)
From this, the lofty status of the teachers and instructors of religion is also made clear.
After the passing of the Noble Prophet (sallallahu alayhi wa sallam) from this world, all of this can only be obtained from the scholars (‘ulama).
And the very office of the Messenger of Allah (sallallahu alayhi wa sallam) was also that of a teacher, as is stated in the Noble Qur’an:
﴿وَيُعَلِّمُهُمُ الكِتـبَ وَالحِكمَةَ﴾ (al-Baqarah: 129)
“(That Prophet) will teach them the Book and wisdom.”
This very wisdom is that understanding of the religion which, in this hadith, has been expressed as "fiqh."