وَاخْتِلَافِ اللَّيْلِ وَالنَّهَارِ
وَمَا أَنزَلَ اللَّهُ مِنَ السَّمَاء مِن رِّزْقٍ
And in the alternation of night and day, and the provision that Allah sends down from the sky,
Allah directs His servants to contemplate His favors and gifts, as well as His great power that is demonstrated by His creating the heavens and the earth and the various types and categories of creatures in them. There are the angels, Jinns, humans, animals, birds, beasts, carnivores, insects and various kinds of sea creatures.
The night and day alternate, each follows the other in succession, never ceasing to come, as decreed. One brings darkness and one brings light. Allah the Exalted also sends down the rain from the clouds when it is most needed. He is calling the rain, `provision', because it is the resource that produces various provisions,
فَأَحْيَا بِهِ الاْأَرْضَ بَعْدَ مَوْتِهَا
and revives therewith the earth after its death,
after it was dry and had no vegetation or life of any kind.
Allah said next,
وَتَصْرِيفِ الرِّيَاحِ
and in the turning about of the winds,
sometimes towards the south and sometimes towards the north. Some are easterly winds and some are westerly winds, some bringing sea breezes and some blow from the land, some coming at night and some by day. Some winds bring rain, some cause pollination and some winds just revive the soul, while some others bear no benefit.
ايَاتٌ لِّقَوْمٍ يَعْقِلُونَ
are signs for a people who understand.
Allah said first
لَاايَاتٍ لِّلْمُوْمِنِينَ
(are signs for the believers),
then
يُوقِنُونَ
(who have faith with certainty),
then
يَعْقِلُونَ
(who understand),
thus ascending from one honorable stage to what is more honorable and higher in grade.
These Ayat are similar to an Ayah in Surah Al-Baqarah,
إِنَّ فِي خَلْقِ السَّمَـوَتِ وَالاٌّرْضِ وَاخْتِلَـفِ اللَّيْلِ وَالنَّهَارِ وَالْفُلْكِ الَّتِى تَجْرِى فِى الْبَحْرِ بِمَا يَنفَعُ النَّاسَ وَمَأ أَنزَلَ اللَّهُ مِنَ السَّمَأءِ مِن مَّأءٍ فَأَحْيَا بِهِ الاٌّرْضَ بَعْدَ مَوْتِهَا وَبَثَّ فِيهَا مِن كُلِّ دَابَّةٍ وَتَصْرِيفِ الرِّيَـحِ وَالسَّحَابِ الْمُسَخَّرِ بَيْنَ السَّمَأءِ وَالَارْضِ لايَـتٍ لِّقَوْمٍ يَعْقِلُونَ
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 which Allah sends down from the sky and makes the earth alive therewith after its death, and the moving creatures of all kinds that He has spread therein, and in the veering of winds and clouds which are held between the sky and the earth, are indeed signs for people of understanding. (2;164