According to the teachings of religion, "TAHDIS" has the meaning of conversation between Allah's angels with the Prophet, or Imam or another person. This subject, since the time of the Prophet (praise and greeting from Allah to Mohammad and his descendants) has propounded and could be perceived as the source of their Knowledge. In the Islamic Society, the belief that after the Prophet, there was no access to Revelation, was seen as equivalent of abstainance to attain Divine Knowledge and all claims of Divine, or acquired Knowledge were seen as equivalent to Prophecy claim. Imams by using "TAHDIS" taught the Shi'i Community that it is possible for a person other than the Prophet to gain access to Revelation through other than the usual ways.
It is clear that the dimensions of this Subject gradually cought the attention of the Shi'is and led to a Shi'i discourse on the Divine Knowledge of the Imams. It should be noted that this belife ecountered difficulties and dangers during the time of the Sadeghin (Imam Bagher and Imam Sadegh), and also had to be controlled so as not to fall into exageration.
Abtahi A H. Historical Review of the development of "Tahdis" among the Shi'is during the first half of the Second century of Hijra. مطالعات تاریخ اسلام 2014; 6 (22) :7-32 URL: http://journal.pte.ac.ir/article-1-205-en.html