Allah says:

[وَلَوْ بَسَطَ اللَّهُ الرِّزْقَ لِعِبَادِهِ لَبَغَوْاْ فِى الاٌّرْضِ]

(And if Allah were to extend the provision for His servants, they would surely rebel in the earth,) means, `if We gave them more provision than they need, this would make them rebel and transgress against one another in an arrogant and insolent manner.'

[وَلَـكِن يُنَزِّلُ بِقَدَرٍ مَّا يَشَآءُ إِنَّهُ بِعِبَادِهِ خَبِيرُ بَصِيرٌ]

(but He sends down by measure as He wills. Verily, He is, in respect of His servants, the Well-Aware, the All-Seer.) means, but He gives them provision according to what is in their best interests, and He knows best about that. So He makes rich those who deserve to be rich, and He makes poor those who deserve to be poor.

[وَهُوَ الَّذِى يُنَزِّلُ الْغَيْثَ مِن بَعْدِ مَا قَنَطُواْ]

(And He it is Who sends down the rain after they have despaired,) means, after the people have given up hope that rain will fall, He sends it down upon them at their time of need. This is like the Ayah:

[وَإِن كَانُواْ مِن قَبْلِ أَن يُنَزَّلَ عَلَيْهِمْ مِّن قَبْلِهِ لَمُبْلِسِينَ ]

(And verily, before that (rain) -- just before it was sent down upon them -- they were in despair!) (30:49)

[وَيَنشُرُ رَحْمَتَهُ]

(and spreads His mercy. ) means, He bestows it upon all the people who live in that region. Qatadah said, "We were told that a man said to `Umar bin Al-Khattab, may Allah be pleased with him, `O Commander of the faithful, no rain has come and the people are in despair.' `Umar, may Allah be pleased with him, said, `Rain will be sent upon you,' and he recited:

[وَهُوَ الَّذِى يُنَزِّلُ الْغَيْثَ مِن بَعْدِ مَا قَنَطُواْ وَيَنشُرُ رَحْمَتَهُ وَهُوَ الْوَلِىُّ الْحَمِيدُ ]

(And He it is Who sends down the rain after they have despaired, and spreads His mercy. And He is the Protector, Worthy of all praise).'' Meaning He is the One Who is in control of His creation, taking care of what will benefit them in this world and the Hereafter, and the consequences of all His decrees and actions are good, for which He is worthy of all praise.

[وَمِنْ ءَايَـتِهِ خَلْقُ السَّمَـوَتِ وَالاٌّرْضِ وَمَا بَثَّ فِيهِمَا مِن دَآبَّةٍ وَهُوَ عَلَى جَمْعِهِمْ إِذَا يَشَآءُ قَدِيرٌ - وَمَآ أَصَـبَكُمْ مِّن مُّصِيبَةٍ فَبِمَا كَسَبَتْ أَيْدِيكُمْ وَيَعْفُواْ عَن كَثِيرٍ - وَمَآ أَنتُمْ بِمُعْجِزِينَ فِى الاٌّرْضِ وَمَا لَكُمْ مِّن دُونِ اللَّهِ مِن وَلِىٍّ وَلاَ نَصِيرٍ ]

(29. And among His Ayat is the creation of the heavens and the earth, and whatever moving creatures He has dispersed in them both. And He is Able to assemble them whenever He wills.) (30. And whatever of misfortune befalls you, it is because of what your hands have earned. And He pardons much.) (31. And you cannot escape from Allah in the earth, and besides Allah you have neither any protector nor any helper.)