Allah informs us about His might, majesty and pride, meaning that all things submit themselves to Him and every created being - animate and inanimate, as well as the responsible - humans and Jinns, and the angels - all humble themselves before Him. He tells us that everything that has a shadow leaning to the right and the left, i.e., in the morning and the evening, is by its shadow, prostrating to Allah. Mujahid said, "When the sun passes its zenith, everything prostrates to Allah, may He be glorified." This was also said by Qatadah, Ad-Dahhak and others.
لِلَّهِ وَهُمْ
(while they are humble) means, they are in a state of humility. Mujahid also said: "The prostration of every thing is its shadow", and he mentioned the mountains and said that their prostrations are their shadows. Abu Ghalib Ash-Shaybani said: "The waves of the sea are its prayers". It is as if reason is attributed to these inanimate objects when they are described as prostrating, so Allah says:
Even the Punishment of the World is Mercy in Disguise
In the verses cited above, after having mentioned various punishments which could seize disbelievers within this world, it was said in the end: فَإِنَّ رَبَّكُمْ لَرَءُوفٌ رَّحِيمٌ (So, indeed your Lord is Very Kind Very Merciful).
First of all, by using the word: رَبّ (Rabb: Lord) here, the hint given is that all these punishments which overtake human beings in this world are there to warn them as part of the dictates of Divine mercy. After that, by introducing the word: رَءُوفٌ(Ra uf: Kind) headed by the intensifying particle lam) that is, the lam of ta'kid), and thus by placing stress on the fact that Allah Ta’ ala was Very Kind and Very Merciful, the hint given was that warnings sent during the life of the world were, in reality, called for by His intrinsic Kindness and Mercy so that heedless men and women would learn from the warning and correct their deeds (before comes 'the last spasm of mass extinction' they themselves are talking about at the closing of the twentieth century, but are still not ready to learn, believe and correct).
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 50–51
Man indulges in arrogance in a world where all the things surrounding him are teaching him lessons in obedience. For example, the shadows of material things. The shadow of a thing standing erect falls on the ground. In this way, it symbolizes kneeling down (sajdah). It shows symbolically how a man should bow down before his Creator. Though angels are not visible to man, the running of this immense universe in the most regulated manner proves that the agents appointed by God to run it are extremely powerful. These angels, in spite of being extraordinarily powerful, are totally obedient to God. If they were not so, the system of the universe would not function continuously with so much precision and uniformity. In view of this, to be entirely correct in his behaviour, man can do no other than surrender himself to God, do obeisance to Him and become His most obedient subject.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.