Read the English translation of ‘Munkidh min al-Dalal’ (Deliverance from Error) by Muhammad Abulaylah.
It is a sort of intellectual autobiography of Imam Ghazali. Imam Ghazali talks about the spiritual crisis he went through and how he set out in quest of certain knowledge about the ultimate questions of life. He examined the beliefs and practices of all religious sects and philosophies prevalent at his time and ultimately found truth and certitude in the way of Sufis. In a very succinct way, he presents the gist of his intellectual and spiritual journey. It’s a must read being one of the most important classical Islamic books.