The Shia School prides itself in opening the door for ijtihad from the first days of Islam, but I will not dwell on its importance here and the evidence for its need to keep up with the changing times, since there is no disagreement on this aspect (although there are different views in defining ijtihad ). Shaheed Al Sadr says: ‘Ijtihad allows the muslims to apply islamic theory to daily life, since pracitcal application cannot happen until ijtihad defines the theory and its details.’ 
The differences in opinion arose with differing views on the role of the mujtahid and the extent of his responsibilities (although the responsibilites are clearly stated in the Quran and narrations as we’ll see below..).
Imam Khomeini’s view on Ijtihad: ‘We have limited ourselves to a small part of juristic laws, and left many aspects untouched and therefore many aspects of ijtihad remain strange to us.’  He saw that the ijtihad being performed at the religious seminaries was not enough to tackle all the issues faced by the muslim nations, due to the wrong understanding of ijtihad and intellectual standstill due to the focus on the individual and not the society as a whole. The solution he proposed was: ‘Islam deals with all aspects of life, and gave corresponding laws for each (aspect).’
This is where the correct understanding of fiqh becomes critical in understanding the correct purpose of ijtihad and the correct role of the mujtahid. And, as always, to establish the correct meaning of any religious concept, we must go to the Quran:
وَمَا كَانَ الْمُؤْمِنُونَ لِيَنفِرُوا كَافَّةً ۚ فَلَوْلَا نَفَرَ مِن كُلِّ فِرْقَةٍ مِّنْهُمْ طَائِفَةٌ لِّيَتَفَقَّهُوا فِي الدِّينِ وَلِيُنذِرُوا قَوْمَهُمْ إِذَا رَجَعُوا إِلَيْهِمْ لَعَلَّهُمْ يَحْذَرُونَ
‘And it does not beseem the believers that they should go forth all together; why should not then a company from every party from 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?’ 
Before talking about the meaning of the word ‘fiqh’ or ‘tafaquh’ in this verse, another important phrase is ‘why should not’ (فَلَوْلَا), which is used as an exhortation to do a certain thing, in this case: ‘to obtain understanding in religion’, i.e. it is obligatory (for all or some) to obtain religious knowledge.
The verse then defines the role of those who obtained religious knowledge to be ‘that they may warn their people when they come back to them’, correlating understanding in religion with warning, deeming knowledge on its own to be insufficient without spreading it to those who lack it. But what does ‘when they come back to them’ mean? They must have gone somewhere to return to their people. It is evident, then, that migration of those tasked with obtaining knowledge and then returning to their people, having gathered all necessary information and experience, is fundamental to ‘warning’ them and providing themselves and others with the tools to counter any (intellectual) threat they might face.
Allamah al-Tabatabai’s view on the verse: ‘Hence it is clear that the intended meaning of ‘becoming learned’ (tafaquh) is to gain an understanding of all religious sciences, whether the roots of the religion or its branches, and not just the practical laws, which is the formal meaning of fiqh amongst religious people. The proof for this is first, ‘to become learned in religion’ and second, ‘and to warn their people…’ because they can only warn their people if they have an understanding of all aspects of the religion, including that which will occasion divine reward or punishment in the Hereafter.’ 
Knowledge in religion (tafaquh) in narrations
The narrations dealing with the importance of knowledge and the obligation of its acquisition are numerous, I will mention just one relevant to our discussion above:
Imam al-Sadiq (as) said: ‘Become learned in religion, for those who do not are desert dwellers (i.e. ignorant and lacking knowledge)’ 
The term ‘desert dwellers’ should not be taken as an insult, as the Quran has given a clear definition for this group in society:
قَالَتِ الْأَعْرَابُ آمَنَّا ۖ قُل لَّمْ تُؤْمِنُوا وَلَـٰكِن قُولُوا أَسْلَمْنَا وَلَمَّا يَدْخُلِ الْإِيمَانُ فِي قُلُوبِكُمْ
‘The dwellers of the desert say: We believe. Say: You do not believe but say, We submit; and faith has not yet entered into your hearts..’ 
The desert dwellers are far removed from the centres of knowledge and culture, which will have an effect on their spiritual and behavioural conduct.
 See: ‘Ijtihad: its meaning, sources, beginning and practice of ra’y’
 Muhammad Baqir al-Sadr: ‘Future directions of the Ijtihad movement’, Al Ghadeer magazine, Dec 1980.
 Imam Ruhollah Khomeini, ‘Islamic Government’, pg65.
 Al Tawbah:122
 Allamah Tabataba’i, Tafsir Al Mizan, Vol9, pg337.
 Usul al Kafi, Vol1, pg31, H6.
 Al Hujurat:14