Mawlana Masihullah Khan Sherwani (Raheemahullah) writes in “Shariat & Tasawwuf”,
Bay’at is a pledge to strive to adhere to and execute the esoteric and exoteric actions of Islam…
Therefore Bay’at refers to the pledge of allegiance that the Seeker takes with the Shaykh that he will not go against the dictates of the Shari’ah. Know that Bay’at is Sunnah.
One is the concept of Bay’at and the other is the concept of Islaah -e- Nafs.
Islaah -e- Nafs refers to the purification of the soul from the bad qualities (Akhlaaqe – Razeelah) and to imbibe within ourselves the good/praiseworthy qualities (Akhlaaqe – Hameedah). Know that Islaah -e- Nafs is Fard (Obligatory) on every mature adult Muslim.
For better understanding refer to the following explanation taken from askimam.org
It is Waajib (necessary) upon every muslim to refine his character, correct his beliefs and in brief, live a life according to Shari’a. This could be attained in many ways such as studying under a teacher, sitting in the gatherings of the pious, taking bay’t to a Shaykh etc. (Fataawa Mahmoodiyya, vol 4, pg 405/414, Farooqiyya)
However, it has always been the divine scheme of Allah Ta’ala that perfection cannot be attained without an expert instructor. Thus, if one intends to lead a life perfectly according to Shari’a, he should submit himself to the guidance and care of an expert instructor in this field i.e. Shaykh. This in essence is known as Bay’at.
If a person feels that he has the ability to lead a life perfectly according to Shari’a, by simply studying under a teacher, researching etc, he may do so. However, experience proves that the most effective method to lead a perfect way of life is to submit oneself to the guidance and care of a Shaykh. Many of our Aslaaf (pious predecessors) despite been high authorities of Islamic knowledge, felt the necessity to submit themselves to a Shaykh and take bay’at.
In fact, bay’at is established in the Quraan and the Ahadith.
Allah Ta’ala mentions: “Indeed, Allah was pleased with the believers when they gave the bay’t to you (Oh Muhammad sallallaahu alayhi wa sallam) under the tree”.[Al-Fath 18]
It is recorded in Sahih Al-Muslim that Auf bin Malik Al-Ashja’ee said: “We were with the Prophet صلى الله عليه وسلّم seven, eight or nine of us, when he said: Will you not make bay’at to the Prophet صلى الله عليه وسلّم ? We stretched our hands and enquired: On what should we make bay’at to you, Oh Prophet of Allah? He said: That you make the ibaadat of Allah, associate nothing with him, perform the five salaat and you listen and obey.” (Shari’a and Tasawwuf, vol 1, pg18)
Is Bay’at Shirk?
“The concept of Bai’at is expressly mentioned in the Quran and Hadith. There are different categories of Bai’at.
One is to express submission to the leader of the Muslims, Ameerul Mo’mineen. This category of Bai’at is compulsory.
The other category of Bai’at is for Islaah (reformation). This category of Bai’at is not compulsory. If a person is able to reform himself independently without the assistance of a spiritual guide, then he may do so. In such an instance, there is no need for Bai’at.
However, generally, a person experiences difficulties in reforming himself and he requires the assistance of an expert to assist him in the reformation process. In order to achieve that, he takes Bai’at as an expression of determination and submission to obey. His spiritual guide then takes it upon himself to guide his Mureed and the Mureed undertakes to obey.
Therefore the purpose of Bai’ at is at most an administrative matter to achieve maximum benefit and results. It is not Shirk. However, we advise, you should exercise caution in choosing your Peer. Apart from him excelling in Taqwa, piety and having the expertise to reform, you too must be comfortable with him and his procedure. You must be able to relate to him and be able to benefit. For that we propose you first keep Islaahi relationship and qualify that with Bai’at later only after you are satisfied. ” taken from Mufti Ebrahim Desai’s website: daralmahmood.org