What is the role of the mind for the muslim?

The role of the mind in this is to understand, comprehend, know the meanings, look into the chains of narration (regarding the sunnah) and it's authenticity. He shouldn't put forward his opinion before the Kitab and sunnah. Rather, it's obligatory that you submit to the Book (Qur'an) and sunnah. It is not for the people of Islam to put forth their intellects or opinions above what the Book and Sunnah have said. No, the intellect follows; it's only job is to ponder, understand, and implement. It is not for him to legislate. Those who legislated from the jahmiyyah, mutazilah, and others doomed themselves and fell into forms of falsehood. That was because they put forth the intellects above the texts (of the Qur'an and Sunnah). And what is obligatory is to make the intellects, hearts, and souls submit to the texts (from the Quran and Sunnah), and that the believer should be a follower of the Book of Allah and that which is authentic of the sunnah of the Messenger of Allah ﷺ. However, he uses his intellect in knowing the meanings, the authenticity or inauthenticity of the hadeeth, to ask the people of knowledge, to look into the paths that lead to that. This is the job of the intellect. As for putting forward his opinion above that which is established from the shari'ah of Allah, then no.