Tafsir of Al-Mu'minoon 23:11

(Who will inherit Al-Firdaws) is an explanatory adjective, an explanatory apposition (‘atf bayan), or a substitute (badal). Regardless of which, it provides a clarification of what they inherit and serves to constrain the inheritance after its initial mention, thereby magnifying it and emphasizing it.

Al-Firdaws is the highest level of Paradise. 'Abd ibn Humayd and al-Tirmidhi—who classified it as hasan sahih gharib—reported from Anas (may Allah be pleased with him) that al-Rubayyi' bint al-Nadir came to the Messenger of Allah (may Allah be pleased with him and grant him peace). Her son, Harithah ibn Suraqah, had been struck on the day of Badr by a stray arrow. She said, "Tell me about Harithah; if he has attained Paradise, I will seek reward and be patient, but if he has not attained Paradise, I will strive in supplication." The Prophet (may Allah be pleased with him and grant him peace) said, "It is gardens within Paradise, and your son has attained the highest Al-Firdaws."

Al-Firdaws is the plateau of Paradise, its center, and its best part. Based on this, there is no conflict regarding the exclusivity [of the inheritance] to which we alluded earlier. For whoever is not characterized by the aforementioned attributes, even if he enters Paradise, does not inherit Al-Firdaws, which is its best part. Even assuming he were to be granted it, he would not truly be called an "inheritor," for that [term] is generally applied only after toil and hardship. [They also] inherit it from the disbelievers, who forfeited it for themselves, for Allah the Exalted created for every person a dwelling in Paradise and a dwelling in Hell.

Sa'id ibn Mansur, Ibn Majah, Ibn Jarir, Ibn al-Mundhir, and others reported from Abu Hurayrah that he said: "The Messenger of Allah (may Allah be pleased with him and grant him peace) said: 'There is not one of you who does not have two dwellings in Paradise and a dwelling in Hell. When he dies and enters the Fire, the people of Paradise inherit his dwelling; that is the meaning of the words of the Exalted: Those are the inheritors.'"

It is said that "inheritance" is a metaphor for entitlement, and this contains a great deal of hyperbole, as inheritance is the strongest of the causes of ownership. However, the first [interpretation] is preferred, as it is the interpretation of the Messenger of Allah (peace and blessings be upon him), as verified by al-Qurtubi.

(They will be therein), meaning in Al-Firdaws, which, according to what Ibn al-Shihnah mentioned, can be treated as either feminine or masculine. Some have mentioned that the feminine gender is used because it is a name for Paradise or its highest tier. The full discussion on Al-Firdaws has already preceded for you.

(Abiding forever): They will never be expelled from it. The sentence is either an incipience (musta'nafah) confirming what preceded it, or a prospective circumstantial clause (hal muqaddarah) pertaining to the subject of "inherit" or its object, as Abu al-Baqa' said, since both are mentioned therein. The meaning of the statement is that they will not die and they will not be expelled from it.