First of all, the words of the righteous predecessors which you have mentioned regarding Istiwaa’ mean that they affirm the attribute of Allaah The Almighty related to His Istiwaa’ over His throne without distorting its wording or meaning, nor denying it, nor asking how it is, nor drawing any resemblance between Allaah and any of His creation.

Therefore, the meaning of Istiwaa’ in language is known; it means, according to the Tafseer (explanation) of the righteous predecessors, height, exaltation and elevation. The affirmation of the meaning of Istiwaa’, in fact, refutes the claims of the Mufawwidhah, who believe in the word itself but not in its meaning. They claim that only Allaah The Almighty knows the meaning of His attributes.

As a matter of fact, when the righteous predecessors said that the manner of Istiwaa’ is inconceivable, this means that only Allaah The Almighty knows its exact nature. This also applies to the exact nature of His hearing, seeing, knowing, coming and descending to the lowest heaven, for it is only He who knows the manner. Knowing the exact nature of the attributes of Allaah The Almighty is part of knowing the exact nature of His essence and Allaah The Almighty Says (what means): {There is nothing like unto Him, and He is the Hearing, the Seeing.} [Quran 42:11]

Second, the rule upon which the Sunnis build their belief concerning this issue is the affirmation of the names and attributes of Allaah The Almighty that have been mentioned in the Quran and in the authentic Sunnah without distorting their wordings or meanings, nor denying them, nor asking how they are, nor drawing any resemblance between Allaah and any of His creation.

In other words, they affirm their meanings linguistically and leave the knowledge of their exact nature to Allaah The Almighty.

Allaah Knows best.