Ibn Kathir
The Proofs for Tawhid
Allah said:
إِنَّ فِي خَلْقِ السَّمَـوَتِ وَالاٌّرْضِ
(Verily, in the creation of the heavens and the earth...)
Therefore, the sky, with its height, intricate design, vastness, the heavenly objects in orbit, and this earth, with its density, its lowlands, mountains, seas, deserts, valleys, and other structures, and beneficial things that it has. Allah continues:
وَاخْتِلَـفِ الَّيْلِ وَالنَّهَارِ
(...and in the alternation of night and day.)
This (the night) comes and then goes followed by the other (the day) which does not delay for even an instant, just as Allah said:
لاَ الشَّمْسُ يَنبَغِى لَهَآ أَن تدْرِكَ القَمَرَ وَلاَ الَّيْلُ سَابِقُ النَّهَارِ وَكُلٌّ فِى فَلَكٍ يَسْبَحُونَ
(It is not for the sun to overtake the moon, nor does the night outstrip the day. They all float, each in an orbit.) (36:40)
Sometimes, the day grows shorter and the night longer, and sometimes vice versa, one takes from the length of the other. Similarly Allah said:
يُولِجُ الَّيْلَ فِى النَّهَارِ وَيُولِجُ النَّهَارَ فِى الَّيْلِ
(Allah merges the night into the day, and He merges the day into the night) (57:6) meaning, He extends the length of one from the other and vice versa. Allah then continues:
وَالْفُلْكِ الَّتِى تَجْرِى فِى الْبَحْرِ بِمَا يَنفَعُ النَّاسَ
(. ..and the ships which sail through the sea with that which is of use to mankind,)
Shaping the sea in this manner, so that it is able to carry ships from one shore to another, so people benefit from what the other region has, and export what they have to them and vice versa.
Allah then continues:
وَمَآ أَنزَلَ اللَّهُ مِنَ السَّمَآءِ مِن مَّآءٍ فَأَحْيَا بِهِ الاٌّرْضَ بَعْدَ مَوْتِهَا
(...and the water (rain) which Allah sends down from the sky and makes the earth alive therewith after its death), which is similar to Allah's statement:
وَءَايَةٌ لَّهُمُ الاٌّرْضُ الْمَيْتَةُ أَحْيَيْنَـهَا وَأَخْرَجْنَا مِنْهَا حَبّاً فَمِنْهُ يَأْكُلُونَ
(And a sign for them is the dead land. We give it life, and We bring forth from it grains, so that they eat thereof.) (36:33), until:
وَمِمَّا لاَ يَعْلَمُونَ
(which they know not.) (36:36)
Allah continues:
وَبَثَّ فِيهَا مِن كُلِّ دَآبَّةٍ
(and the moving (living) creatures of all kinds that He has scattered therein,) meaning, in various shapes, colors, uses and sizes, whether small or large. Allah knows all that, sustains it, and nothing is concealed from Him. Similarly, Allah said:
وَمَا مِن دَآبَّةٍ فِي الاٌّرْضِ إِلاَّ عَلَى اللَّهِ رِزْقُهَا وَيَعْلَمُ مُسْتَقَرَّهَا وَمُسْتَوْدَعَهَا كُلٌّ فِى كِتَابٍ مُّبِينٍ
(And no moving (living) creature is there on earth but its provision is due from Allah. And He knows its dwelling place and its deposit (in the uterus or grave). All is in a Clear Book (Al-Lawh Al-Mahfuz ـ the Book of Decrees with Allah).) (11:6)
وَتَصْرِيفِ الرِّيَـحِ
(...and in the veering of winds...)
Sometimes, the wind brings mercy and sometimes torment. Sometimes it brings the good news of the clouds that follow it, sometimes it leads the clouds, herding them, scattering them or directing them. Sometimes, the wind comes from the north (the northern wind), and sometimes from the south, sometimes from the east, and striking the front of the Ka`bah, sometimes from the west, striking its back. There are many books about the wind rain, stars and the regulations related to them, but here is not the place to elaborate on that, and Allah knows best.
Allah continues:
وَالسَّحَابِ الْمُسَخَّرِ بَيْنَ السَّمَآءِ وَالأَرْضِ
(...and clouds which are held between the sky and the earth,)
The clouds run between the sky and the earth to wherever Allah wills of lands and areas.
Allah said next:
لآيَـتٍ لِّقَوْمٍ يَعْقِلُونَ
(...are indeed Ayat for people of understanding,) meaning, all these things are clear signs that testify to Allah's Oneness. Similarly, Allah said:
إِنَّ فِى خَلْقِ السَّمَـوَتِ وَالاٌّرْضِ وَاخْتِلَـفِ الَّيْلِ وَالنَّهَارِ لاّيَـتٍ لاٌّوْلِى الاٌّلْبَـبِ - الَّذِينَ يَذْكُرُونَ اللَّهَ قِيَـماً وَقُعُوداً وَعَلَى جُنُوبِهِمْ وَيَتَفَكَّرُونَ فِى خَلْقِ السَّمَـوَتِ وَالاٌّرْضِ رَبَّنَآ مَا خَلَقْتَ هَذا بَـطِلاً سُبْحَـنَكَ فَقِنَا عَذَابَ النَّارِ
(Verily, in the creation of the heavens and the earth, and in the alternation of night and day, there are indeed signs for men of understanding. Those who remember Allah (always, and in prayers) standing, sitting, and lying down on their sides, and think deeply about the creation of the heavens and the earth, (saying): "Our Lord! You have not created (all) this without purpose, glory to You! (Exalted are You above all that they associate with You as partners). Give us salvation from the torment of the Fire.") (3:190, 191)