The idea of Jurisprudence and Taqlid (Imitation)!

Imam Sadiq (p) said: “Burid bin Muawiyah al-Ajali, Abi Basir Layth al-Bakhtari alMuradi, Muhammad bin Muslim and Zararah will be given the glad tidings of Heaven. They believe in Allah about the obligatory actions and forbidden ones. The line of prophethood would have discontinued if it were not for them.” and he (p) considered them mujtahids who had the capability of deriving verdicts from the Quran and prophetic (p) traditions.

Sometimes Imam (p) would order them to practice it, for example, he (p) said: “It is upon us to tell you the principles and it is upon you to branch them out.” He (p) also told people to refer to some of his companions in religious rulings, like Yumis bin Abd al-Rahman. Someone asked the Imam (p): “It is not possible for me to come to you and ask everything that I need about religious sciences. Is Yunis bin Abd al-Rahman trustworthy; can I take whatever I need from him?” The Imam (p) answered: “Yes.” He (p) also ordered some of his companions to give religious verdicts, such as Aban bin Taghlib. The Imam (p) told him: “Sit in Medina's mosque and give religious verdicts to the people. Verily I love to see my Shia to be like you.

Source: The Basics of Islamic Jurisprudence