Idealist- Realist > Status Update

Im not wholly convinced on the Sufist's principle that acquiring the highest level of faith is the way to certainty or certitude of Reality. Their notion of INFALLIBLE IMAM always provokes my thought. From the previous chapter, it tells us that al-Ghazzali have reached the level HAQQ-AL-YAQIN that implies that this the level of certitude. I wanna see if the author give a space for explanation of this.