It is true that knowledge is light and ignorance is darkness; and it is also obvious that light is better than darkness, but lights are of different types. It is clear that knowledge is more important when it deals with excellent issues and when its results are beneficial to man.
Because the knowledge of religion deals with either opinions and right knowledge or with Divine commandments and individual and social laws or deals with ethical commands, and since these affairs belong to the sacred religion and are the foundations of man's prosperity both here and in the Hereafter, the Prophet (S) has considered this branch of human knowledge as knowledge and the rest of human knowledge as "Fadl" or divine grace.
"اِنّما العِلمُ ثَلاثَة: آيةٌ مُحكَمَة اَو فَرِيضَةٌ عَادِلَةٌ او سُنَّةٌ قَائِمَةٌ وَمَا خَلاهُنَّ فَهُوَ فَضْل"404
“Knowledge is only of three kinds: (knowledge of) the firm verses (of the Qur’an), (knowledge of) the equitable division of obligatory shares of inheritance, and (knowledge of) the established Sunnah (i.e. those principles which are based on clear reasoning, the commandments which are based on justice, and ethics and guidelines for life which are always constant). Whatever is other than that is surplus.”1
Thus, "tafaqquh" or becoming learned in religion, which is the study of ideological, legal and ethical issues, has always been the pivotal question with the religion leaders. As we see, Imam (as), in the above expression, encourages his son to learn it and Imam al-Kadhim (as) too asks his followers to do the same thing:
"Become learned in the religion of God, for the acquisition of knowledge is the key to insight, the perfection of worship and the means to attaining exalted stations and sublime ranks in religion and in this world. The excellence of the religious scholar2 over the worshipper is like the excellence of the sun over the stars. God does not approve of the deeds of one who does not become learned in his religion."3
And the Great Prophet (S) of Islam has said: “When God wishes good for a servant, He makes him learned in religion.”4
Imam Sadiq (as), as well, has said, concerning this issue: "Become learned in religion, because anybody among you who does not become learned in religion is (like) a Bedouin. God has said in the Qur’an:
‘Why should not then a company from every party among them go forth that they may apply themselves to obtain understanding in religion, and that they may warn their people when they come back to them that they may be cautious (9:122)?’"5
1. This tradition is interpreted in some other forms, as well. For further information, refer to the “History of Islamic culture and civilization”, by this writer, P 55.
2. As Majlisi and others have explained: by Faqih or jurisprudent is meant one who has insight into different dimensions of religion. (Mir’at al-‘Uqul, vol.1, p.100; Shafi, p.21).
3. Bihar, vol.78, p.321.
4. Kanz al-Ummal, vol.10, p.137, Hadith 28690.
5. Usul al-Kafi, vol.1, p.31. .