Verily, in the creation of the heavens and the earth, and in the alternation of night and day, and the ships which sail through the sea with that which is of use to mankind, and the water (rain) which Allah sends down from the sky and makes the earth alive therewith after its death, and the moving (living) creatures of all kinds that He has scattered therein, and in the veering of winds and clouds which are held between the sky and the earth, are indeed Ayat (proofs, evidences, signs, etc.) for people of understanding (164)
The Proofs for Tawhid
Allah said:
إِنَّ فِي خَلْقِ السَّمَاوَاتِ وَالْأَرْضِ
(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:
وَاخْتِلَافِ اللَّيْلِ 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:
لَا الشَّمْسُ يَنبَغِي لَهَا أَن تُدْرِكَ الْقَمَرَ وَلَا اللَّيْلُ سَابِقُ النَّهَارِ وَكُلٌّ فِي 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 اللَّيْلَ فِي النَّهَارِ وَيُولِجُ النَّهَارَ فِي اللَّيْلِ
(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 الَّتِي تَجْرِي فِي 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:
وَمَا أَنزَلَ اللَّهُ مِنَ السَّمَاءِ مِن مَّاءٍ فَأَحْيَا بِهِ الْأَرْضَ 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:
وَآيَةٌ لَّهُمُ الْأَرْضُ الْمَيْتَةُ أَحْيَيْنَاهَا وَأَخْرَجْنَا مِنْهَا حَبًّا 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 لَا يَعْلَمُونَ
(which they know not.)(36:36)
Allah continues:
وَبَثَّ فِيهَا مِن كُلِّ دَابَّةٍ
(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 دَابَّةٍ فِي الْأَرْضِ إِلَّا عَلَى اللَّهِ رِزْقُهَا وَيَعْلَمُ مُسْتَقَرَّهَا وَمُسْتَوْدَعَهَا كُلٌّ فِي 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 الرِّيَاحِ
(...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 السَّمَاءِ وَالْأَرْضِ
(...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:
لَآيَاتٍ 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 فِي خَلْقِ السَّمَاوَاتِ وَالْأَرْضِ وَاخْتِلَافِ اللَّيْلِ وَالنَّهَارِ لَآيَاتٍ لِّأُولِي الْأَلْبَابِ - الَّذِينَ يَذْكُرُونَ اللَّهَ قِيَامًا وَقُعُودًا وَعَلَىٰ جُنُوبِهِمْ وَيَتَفَكَّرُونَ فِي خَلْقِ السَّمَاوَاتِ وَالْأَرْضِ رَبَّنَا مَا خَلَقْتَ هَٰذَا بَاطِلًا سُبْحَانَكَ 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)
Now in Verse 164, there is a series of signs and proofs in support of the premise that Allah Almighty is really One. Stated simply, these can be grasped by the learned and the ignorant alike. How can one bypass the wonder of the creation of the heavens and the earth? Who can ignore the constant alternation of the night and the day? The message is simple and clear. Their origination and their perpetuity is the work of His perfect power alone and that there is absolutely no being other than Him who can take that credit.
Similarly, the movement of boats on the surface of waters, is a formidable indicator of Allah's power which gave water, a substance so liquid and fluid, the property of lifting on its back ships which carry tons and tons of weight all the way from the East to the West. Then, there is the movement of winds which Allah harnesses into the service of man, and in His wisdom, keeps changing their direction. These are great signs; they tell us that they were created and operated by a supreme being, the One who is All-Knowing, All-Aware, All-Wise. If the substance of water was not given a state in which the molecules move freely among themselves while remaining in one mass, a functional fluidity in other words, all this maritime activity would not be there. Even if this fluidity of sea-surface was there, help from winds was still needed in order to cover all those thousands of nautical miles across the seas of the world. The Holy Qur'an has summarized the subject by saying:
إِن يَشَأْ يُسْكِنِ الرِّيحَ فَيَظْلَلْنَ رَوَاكِدَ عَلَىٰ ظَهْرِهِ
"If He wills, He can still the winds, then, ships shall remain standing on the back of the seas." (42:33)
The use of the expression بِمَا يَنفَعُ النَّاسَ :'with what benefits men' points out to the countless benefits that accrue to human beings when they mutually trade their goods through sea freighters. It is interesting to keep in mind the variations these benefits take from country to country and from age to age.
Then comes the marvel of water descending from the sky, drop by drop, released in a measure and manner that it hurts nothing. If it always came in the form of a flood, nothing would have survived, man or animal or things. Then, the raining of water is not all; it is the storage of water on earth that baffles the human ingenuity. Risking a simplicity, let us imagine if everyone was asked to store for personal use a quota of water for six month, how would everyone manage that? Even if such an impossible storage was somehow done, how could it be made to remain potable and hygienic all this time? Allah Almighty, in His infinite mercy, took care of this too. The Holy Qur'an says:
فَأَسْكَنَّاهُ فِي الْأَرْضِ ۖ وَإِنَّا عَلَىٰ ذَهَابٍ بِهِ لَقَادِرُونَ
'Then, We made water stay in the earth, although, We were capable of letting it flow away' (23:18)
But, nature did not allow this to happen. For the inhabitants of the earth, human and animal, water was stored in ponds and lakes openly. Then, the same water was lowered into the earth under the mountains and valleys in the form of an unsensed network of hidden pipelines of water accessible to everyone taking the trouble of digging and finding water. Further still, is it not that a huge sea of ice was stored out on top of the mountain ranges which is secure against spoilage and melts out slowly reaching all over the world through nature's own water lines.
To sum up, it can be said that Allah's Oneness has been proved in these verses with the citation of some manifestations of His perfect power. Commentators of the Qur'an have taken up this subject in great details. Those interested may see al-Jassas, al-Qurtubi and others.