Allah's Knowledge, Power and Kingdom are Limitless
هُوَ الَّذِي خَلَقَ السَّمَاوَاتِ وَالْأَرْضَ فِي سِتَّةِ أَيَّامٍ ثُمَّ اسْتَوَى عَلَى الْعَرْشِ ...
He it is Who created the heavens and the earth in six Days and then rose (Istawa) over the Throne.
Allah the Exalted states that He created the heavens and earth, and all that is between them, in six Days and then rose over the Throne after He created them. We discussed this before in the explanation of Surah Al-A`raf, so it is not necessary to repeat the meaning here.
... يَعْلَمُ مَا يَلِجُ فِي الْأَرْضِ ...
He knows what goes into the earth,
indicates His knowledge in the amount of seeds and drops of water that enter inside the earth's surface,
... وَمَا يَخْرُجُ مِنْهَا ...
and what comes forth from it,
of plants, vegetation and fruits.
Allah the Exalted said in another Ayah,
وَعِندَهُ مَفَاتِحُ الْغَيْبِ لاَ يَعْلَمُهَآ إِلاَّ هُوَ وَيَعْلَمُ مَا فِى الْبَرِّ وَالْبَحْرِ وَمَا تَسْقُطُ مِن وَرَقَةٍ إِلاَّ يَعْلَمُهَا وَلاَ حَبَّةٍ فِى ظُلُمَـتِ الاٌّرْضِ وَلاَ رَطْبٍ وَلاَ يَابِسٍ إِلاَّ فِى كِتَـبٍ مُّبِينٍ
And with Him are the keys of all that is hidden, none knows them but He. And He knows whatever there is in the land and in the sea; not a leaf falls, but He knows it. There is not a grain in the darkness of the earth nor anything fresh or dry, but is written in a Clear Record. (6:59)
... وَمَا يَنزِلُ مِنَ السَّمَاء ....
and what descends from the heaven,
pertains to rain, snow, hail and whatever Allah decides descends from heaven of decisions and commandments brought down by the honorable angels.
.. وَمَا يَعْرُجُ فِيهَا ...
and what ascends thereto, (refers to angels and deeds).
In the Sahih, there is a Hadith in which the Prophet said,
يُرْفَعُ إِلَيْهِ عَمَلُ اللَّيْلِ قَبْلَ النَّهَارِ، وَعَمَلُ النَّهَارِ قَبْلَ اللَّيْل
To Him ascend the deeds of the night before the day falls and the deeds of the day before the night falls.
... وَهُوَ مَعَكُمْ أَيْنَ مَا كُنتُمْ وَاللَّهُ بِمَا تَعْمَلُونَ بَصِيرٌ ﴿٤﴾
And He is with you wheresoever you may be. And Allah is the All-Seer of what you do.
meaning, He is watching over you and witnessing your deeds wherever you may be, on land or at sea, during the night or the day, at home or in open areas or deserts. All of that is the same before His knowledge and all of it is under His sight and hearing. He hears your speech and sees where you are. He knows your secrets and your public statements,
أَلا إِنَّهُمْ يَثْنُونَ صُدُورَهُمْ لِيَسْتَخْفُواْ مِنْهُ أَلا حِينَ يَسْتَغْشُونَ ثِيَابَهُمْ يَعْلَمُ مَا يُسِرُّونَ وَمَا يُعْلِنُونَ إِنَّهُ عَلِيمٌ بِذَاتِ الصُّدُورِ
No doubt! They did fold up their breasts, that they may hide from Him. Surely, even when they cover themselves with their garments, He knows what they conceal and what they reveal. Verily, He is the All-Knower of the (secrets) of the breasts. (11:5)
Allah the Exalted said,
سَوَآءٌ مِّنْكُمْ مَّنْ أَسَرَّ الْقَوْلَ وَمَنْ جَهَرَ بِهِ وَمَنْ هُوَ مُسْتَخْفٍ بِالَّيْلِ وَسَارِبٌ بِالنَّهَارِ
It is the same (to Him) whether any of you conceals his speech or declares it openly, whether he be hid by night or goes forth freely by day. (13:10)
Surely, there is no deity worthy of worship, except Allah.
In the Sahih, there is a Hadith in which the Messenger of Allah answered Jibril, when he asked him about Ihsan:
أَنْ تَعْبُدَ اللهَ كَأَنَّكَ تَرَاهُ، فَإِنْ لَمْ تَكُنْ تَرَاهُ فَإِنَّهُ يَرَاك
To worship Allah as if you see Him, and even though you cannot see Him, He surely sees you.
Tafsir Ibn Kathir