Commentary
The word: مَقَالِيدُ (maqalid) in: لَّهُ مَقَالِيدُ السَّمَاوَاتِ وَالْأَرْضِ (To Him belong the keys to the heavens and the earth.- Az-Zumar 39:63 ⧉) is the plural form of: مِقلاد (miqlad) or: مِقلِید (miqlid) meaning a key. It has been said that this word has really been Arabicized from the Persian language. In Persian, a key is called کَلِید (kalid). When Arabicized, it became: اِقلِید (iqlid) with its plural being: مَقَالِيدُ (maqalid) (Ruh-ul-Ma’ ani). Having keys in one's hand denotes ownership, possession and the ability to dispense at will. Therefore, the sense of the verse is that the keys to whatever treasures lie hidden in the heavens and the earth are in the hands of Allah and He alone is the custodian and the dispenser in that it is He who gives whenever He wills to whomever He wills and as much as He wills - and would just not give to anyone He so wills.
And in some narrations of Hadith, the third kalimah, that is: سُبحَانَ اللہِ وَالحَمدُ للہِ وَ لا إلہ إلا اللہُ و اللہُ اَکبَر وَلَاحولَ وَلَا قُوَّۃَ اِلَّا بِاللہِ اَلعَلِیِّ العَظِیم (Pure is Allah and Praised is Allah and there is no god worthy of worship but Allah and Allah is Great and there is no strength and there is no power except from Allah, the High, the Great) has been called: مَقَالِيدُ السَّمَاوَاتِ وَالْأَرْضِ ('the keys to the heavens and the earth' - Az-Zumar 39:63 ⧉). The outcome is: One who recites this kalimah, mornings and evenings, is blessed by Allah Ta’ ala from the treasures of the heavens and the earth. Ibn-ul-Jawzi has declared these narrations to be: موضوع (mawdu': fabricated, forged). But, other Hadith experts have rated these as weak ضَعِیف (da` if) ahadith that can be relied
upon in the matter of the merits of good deeds. (Ruh-ul-Ma’ ani)