At present we are living in the period of Greater Occultation which is the period of “general deputyship”. That is, guidance of the Shiites is an obligation as well as a responsibility of the grand jurists and prominent religious scholars who bear the necessary qualifications and the eligibility to guide people, and it is also the duty and obligation of the people to follow and obey them. As for why the Imam of Time (ajt) does not author a book so that people and religious scholars may turn to it for guidance, there can be many reasons some of which are enumerated as under:
1. The Imam of Time (ajt) has gone into occultation at the behest of God and on account of certain expediencies and reasons. One of the reasons behind the occultation of the Imam (ajt) is lack of preparation. If mankind is not prepared to accept the Imam, then do they have the preparation to accept the Imam’s book? Man’s problem is not the absence of a book by the Imam. If mankind had the necessary preparation, the present commands and injunctions of the Quran and those of the Ahlulbayt (a.s.) would be sufficient.
2- Since there is an expediency in the occultation of the Imam of Time (ajt) and in view of the characteristics of the time of absence and the inaccessibility of the Imam of Time (ajt) to all, if a book were supposed to be written by the Imam during this time, there would have been many people claiming to have the book, so they would relate their sayings to it as a consequence of which it would become difficult to distinguish right from wrong. A good example of the negative consequences can be the pseudo claimants of communication and meeting with the Imam (ajt) leading some people astray and misusing them.
3- The occultation of the Imam (ajt) is outwardly and external in the sense that the people’s spiritual communication with the people have not been ceased. It has been stated in a tradition from the Prophet (pbuh) about the occultation of the Imam of Time (ajt) that: “He is like a sun hidden behind the cloud; he is not seen but the people still benefit from him.” Therefore, the Imam always oversees the situation and he guides people wherever he deems it appropriate. So far, the affairs have been going on as such and the Imam has never left the people on to themselves. Obviously, guidance of people is not restricted to writing a book as there are many a number of ways through which they can be led and guided in the right path.
 - That is because Islam is the last and the most perfect religion, and the Holy Prophet, peace be upon him and his progeny, is the Last of Prophets. Whatever has been necessary to be explained was revealed to the Prophet and gathered in the Quran. Likewise, whatever has been necessary to interpret and expatiate upon the verses has been explained by the Holy Prophet (pbuh) and the Infallible Imams until the time of Imam Mahdi – may Allah hasten his reappearance. When it comes to new occurrences, the Imam of Time (ajt) has pointed out the duties and obligations of the people by saying: “As for the new occurrences, you should turn to the narrators of our hadith because they are my proofs on you and I am God’s proof on them.
"اما الحوادث الواقعه فارجعوا فیها الی رواة حدیثنا ، فانهم حجتی علیکم و انا حجة الله علیهم "
Wasail al-Shi’ah, vol.27, pg.140, 33424. Since, it is not possible, during this time, to extract all the jurisprudential rules from the Quran and Sunnah (prophetic tradition), special juristic principles have been set by Shiite’s infallible Imams (a.s.) for rational analysis within the framework of Quran and the Sunnah of the Holy Prophet (pbuh) based on which a qualified jurist embarks on inferring and deducing Shari’ah laws.
 - غَیْرُ وَاحِدٍ عَنْ مُحَمَّدِ بْنِ هَمَّامٍ عَنِ الْفَزَارِیِّ عَنِ الْحَسَنِ بْنِ مُحَمَّدِ بْنِ سَمَاعَةَ عَنْ أَحْمَدَ بْنِ الْحَارِثِ عَنِ الْمُفَضَّلِ عَنِ ابْنِ ظَبْیَانَ عَنْ جَابِرٍ الْجُعْفِیِعَنْ جَابِرٍ الْأَنْصَارِیِّ أَنَّهُ سَأَلَ النَّبِیَّ ص هَلْ یَنْتَفِعُ الشِّیعَةُ بِالْقَائِمِ ع فِی غَیْبَتِهِ فَقَالَ ص إِی وَ الَّذِی بَعَثَنِی بِالنُّبُوَّةِ إِنَّهُمْ لَیَنْتَفِعُونَ بِهِ وَ یَسْتَضِیئُونَ بِنُورِ وَلَایَتِهِ فِی غَیْبَتِهِ کَانْتِفَاعِ النَّاسِ بِالشَّمْسِ وَ إِنْ جَلَّلَهَا السَّحَابُ.
Behar al-Anwar, vol.52, pg.92.