Why do Ismailis Perform Du'a Karavi or Mubay'ah?

Du'a Karavi is the embodiment of a Qur'anic practice

This article will be very helpful in connecting some of the present day Isma'ili rituals performed in Jamatkhana to the Qur'an. A simple example is this verse of the Qur'an which states:

"O ye who have faith! When you privately consult the Messenger, then present an offering (ṣadaqah) before your private consultation. That will be best for you, and purer for you. But if you find not (the means), God is Oft-Forgiving, Most Merciful."
- Holy Qur’ān 58:12

If you think about it carefully, our current practice of Du'a Karavi (also called Mubay'ah) - where a murid approaches the Mukhi Sahib at the Paat (who represents the Imam while ceremonies/rituals are ongoing in the Jamatkhana), presents on offering (today it would be in the form of currency), and receive the blessings and prayers of the Imam - can be rooted in the above Qur'anic verse which instructs the believers to submit an offering when they meet with the Prophet Muhammad. Now the Isma'ili community is spread out over many continents and has grown to be in the millions. Therefore the Imam cannot physically be present to accept the offerings of all murids and why representatives (Mukhi/Kamadia Saheb) are there to accept them on behalf of the Imam and convey blessings to the murids on behalf of the Imam.

"If, rightly, the Muslims have kept till now to the forms of prayer and fasting at the time of the Prophet, it should not be forgotten that it is not the forms of prayer and fasting that have been commanded, but the facts, and we are entitled to adjust the forms to the facts of life as circumstances changed. It is the same Prophet who advises his followers ever to remain  Ibnu’l-Waqt (i.e. children of the time and period in which they were on earth), and it must be the natural ambition of every Muslim to practice and represent his Faith according to the standard of the  Waqt or space-time.”
 – Imam Sultan Muhammad Shah Aga Khan III,
(Foreword to Muhammad: A Mercy To all the Nations by Al-Hajji Qassim Jairazbhoy,  Read Here)

Mubay'ah is clearly rooted to the concept of Bay'ah which is also rooted in the Qur'an. In Qur’ān 48:10 – referring to the Believer’s placing their hands under the Prophet Muḥammad’s hands in the act of bay‘ah, the Qur’ān states that “the Hand of God is upon their hands.” This is significant because in physical terms, it was the Prophet Muḥammad’s hand which was placed upon the hands of the Believers. But the Qur’ān attributed to entire affair to God.