Showing the Triviality of the Worldly Life and encouraging Spending
Expressing the insignificance and worthlessness of the worldly life, Allah says,
إِنَّمَا الْحَيَوةُ الدُّنْيَا لَعِبٌ وَلَهْوٌ
(This worldly life is only amusement and diversion.) which means that such is its outcome, except for that which is done for the sake of Allah. Because of this, Allah says,
وَإِن تُؤْمِنُواْ وَتَتَّقُواْ يُؤْتِكُمْ أُجُورَكُمْ وَلاَ يَسْـَلْكُمْ أَمْوَلَكُمْ
(And if you believe and have Taqwa of Allah, He will grant you your rewards, and will not ask from you (to sacrifice all of) your possessions.) meaning, He is in no need of you, and asks you for nothing. He only ordained giving charity from your wealth so that you would help your needy brothers. The benefit of that would then come back to you, as well as the rewards. Allah then says,
ؤإِن يَسْـَلْكُمُوهَا فَيُحْفِكُمْ تَبْخَلُواْ
(If He would demand of you all of it and urge you, you would withhold.) meaning, if He pressures you much, you would become stingy.
وَيُخْرِجْ أَضْغَـنَكُمْ
(And He will expose your (secret) ill--wills.) Qatadah said, "Allah knows that extracting wealth (i.e., money from people) brings about ill-wills. " Indeed, Qatadah has said the truth, because money is dear to the people, and they do not spend it except in things that are dearer to them than it. Allah then says,
هَآ أَنتُمْ هَـؤُلاَءِ تُدْعَوْنَ لِتُنفِقُواْ فِى سَبِيلِ اللَّهِ فَمِنكُم مَّن
(Here you are now invited to spend in Allah's cause; but among you are those who withhold (stingily).) meaning, they refuse to spend. Allah continues,
يَبْخَلُ وَمَن يَبْخَلْ فَإِنَّمَا يَبْخَلُ عَن
(And whoever acts stingily is but stingy toward himself.) meaning, he only reduces his own rewards, and the bad outcome of that will come back to him.
نَّفْسِهِ وَاللَّهُ
(For Allah is indeed Al-Ghani) Allah is in need of nothing else, whereas everything is ever in need of Him. Thus, Allah says,
الْغَنِىُّ وَأَنتُمُ
(while you are the needy.) meaning, specifically of Him. The description of Allah as Al-Ghani (in no need) is a necessary description of Allah; on the other hand, the description of the creation as Faqr (needy) is a necessary description for them that they cannot avoid. Allah then says,
وَإِن تَتَوَلَّوْاْ
(And if you turn away, ) which means, if you turn away from obeying Him and adhering to His Laws.
تَتَوَلَّوْاْ يَسْتَبْدِلْ قَوْماً غَيْرَكُمْ ثُمَّ لاَ يَكُونُواْ
(He will replace you with other people; then they will not be like you.) meaning, rather, they will be people who will listen to Him and obey His commands. This concludes the Tafsir of Surat Al-Qital. And Allah is worthy of all praise and gratitude.
Tafsir Ibn Kathir (abridged, English).