Imam Rabbani Shaikh Ahmed Sirhindi (Allah have mercy on him) wrote,
Tasawwuf is not intended to obtain things other than the faith of Ahl-as-Sunnah and (follow) the commands of the Shariah.
Tasawwuf is intended to make the faith of Ahl-as-sunnah secure, conscientious and firm, lest it should be undermined by things bringing doubt.
The faith which is strengthened through the intellect, through evidence and proofs cannot be so firm. Allah declares: “Listen, the hearts find peace only in the remembrance of Allah” 13:28
The second purpose of Tasawwuf is to facilitate worshiping, to bring about enthusiasm, and to do away with the indolence, the reluctance inherent in the nafs-i ammara.
It ought to be realized well that clinging to Tasawwuf is not intended to acquire the ability to see what others do not know, to inform others with the unknown, to perceive lights (nur), spirits, or to enjoy exhilarating dreams. All these are in vain, useless things. What is not in the everyday light, in the various colors, in the natural beauties, that should coax man to leave these and look for other things at the cost of suffering so many inconveniences? After all, both this light and those effulgence, both these beautiful shapes and those other things are all the creations of Allah and bear witnesses to His existence and to the fact that He is the Almighty.’
Maktubaat Imam Rabbani ra, volume 1, letter 266