Allah states that He has perfect knowledge of the good deeds performed by all of His creation, such as charity and various vows, and He rewards tremendously for these deeds, provided they are performed seeking His Face and His promise. Allah also warns those who do not work in his obedience, but instead disobey His command, reject His revelation and worship others besides Him:
وَمَا لِلظَّـلِمِينَ مِنْ أَنصَارٍ
(And for the wrongdoers there are no helpers.) meaning, who will save them from Allah's anger and torment on the Day of Resurrection.
Allah said,
إِن تُبْدُواْ الصَّدَقَـتِ فَنِعِمَّا هِىَ
(If you disclose your Sadaqat, it is well) meaning, "It is well if you make known the charity that you give away."
Allah's statement,
وَإِن تُخْفُوهَا وَتُؤْتُوهَا الْفُقَرَآءَ فَهُوَ خَيْرٌ لَّكُمْ
(But if you conceal them and give them to the poor, that is better for you.) this indicates that concealing charity is better than disclosing it, because it protects one from showing off and boasting. However, if there is an apparent wisdom behind disclosing the charity, such as the people imitating this righteous act, then disclosing it becomes better than concealing it. The Messenger of Allah ﷺ said,
«الْجَاهِرُ بِالْقُرْآنِ كَالْجَاهِرِ بِالصَّدَقَةِ، وَالْمُسِرُّ بِالْقُرآنِ كَالْمُسِرِّ بِالصَّدَقَة»
(He who utters aloud Qur'anic recitation is just like he who discloses charity acts. He who conceals Qur'anic recitation is just like he who conceals charity acts.)
The Ayah indicates that it is better that acts of charity be concealed, as reiterated by the Hadith that the Two Sahihs recorded from Abu Hurayrah that the Messenger of Allah ﷺ said,
«سَبْعَةٌ يُظِلُّهُمُ اللهُ فِي ظِلِّهِ يَوْمَ لَا ظِلَّ إلَّا ظِلُّهُ: إِمَامٌ عَادِلٌ، وَشَابٌّ نَشَأَ فِي عِبَادَةِ اللهِ، وَرَجُلَانِ تَحَابَّا فِي اللهِ،اجْتَمَعَا عَلَيْهِ وَتَفَرَّقَا عَلَيْهِ، وَرَجُلٌ قَلْبُهُ مُعَلَّقٌ بِالْمَسْجِدِ، إِذَا خَرَجَ مِنْهُ حَتَّى يَرْجِعَ إِلَيْهِ، وَرَجُلٌ ذَكَرَ اللهَ خَالِيًا فَفَاضَتْ عَيْنَاهُ، وَرَجُلٌ دَعَتْهُ امْرَأَةٌ ذَاتُ مَنْصِبٍ وَجَمَالٍ، فَقَالَ: إِنِّي أَخَافُ اللهَ رَبَّ الْعَالَمِينَ، وَرَجُلٌ تَصَدَّقَ بِصَدَقَةٍ فَأَخْفَاهَا، حَتَّى لَا تَعْلَمَ شِمَالُهُ مَا تُنْفِقُ يَمِينُه»
(Allah will give shade to seven on the Day when there will be no shade but His. (They are:) a just ruler, a youth who has been brought up in the worship of Allah, two persons who love each other only for Allah's sake who meet and part in Allah's cause only, a man whose heart is attached to the Masjids from the time he departs the Masjid until he returns to it, a person who remembers Allah in seclusion and his eyes are then flooded with tears, a man who refuses the call of a charming woman of noble birth for illicit intercourse with her and says, `I fear Allah, Lord of the worlds', and a man who gives charitable gifts so secretly that his left hand does not know what his right hand has given.)
Allah's statement,
وَيُكَفِّرُ عَنكُم مِّن سَيِّئَاتِكُمْ
((Allah) will expiate you some of your sins) means, in return for giving away charity, especially if it was concealed. Therefore, you will gain goodness by your rank being raised, and your sins being forgiven.
Allah's statement,
وَاللَّهُ بِمَا تَعْمَلُونَ خَبِيرٌ
(And Allah is Well-Acquainted with what you do) means, "No good deed that you perform escapes His knowledge, and He shall reward for it."