[Who is it that is Firmly Grounded in Knowledge]

Answer – and with Allah is success: The one who is firmly grounded in knowledge is he whose knowledge of Allah, exalted is He, has become well-established: [knowledge] of what He deserves of majesty and perfection, and of what He is exalted above of likeness and equal, and of the attributes of originated things and the committing of vile acts, and so on.
Together with his firmly established knowledge of the language of the Qur’an, and his distinguishing between the definitive (muhkam) and the ambiguous (mutashabih), the explicit texts and the apparent meanings, the general and the specific, the absolute and the restricted, the abrogating and the abrogated, and so on.
In addition to his knowledge of and familiarity with the doctrines of the pious predecessors from the Ahl al-Bayt (Peace be upon them) and others from among the scholars of the Companions and the Followers.
And along with all of this, it is necessary that he be among the people of truth, the people of God-consciousness, certainty, and fear of Allah, Lord of the worlds. Whoever is such is among those who are firmly grounded in knowledge.
Allah, exalted is He, has said: "And those who strive for Us – We will surely guide them to Our ways; and indeed Allah is with the doers of good" [al-‘Ankabut], and He, glorified is He, said: "And fear Allah, and Allah will teach you" [al-Baqarah:282].

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3