If Allah knows any good in your hearts, He will give you something better than what has been taken from you

  يَا أَيُّهَا النَّبِيُّ قُلْ لِمَنْ فِي أَيْدِيكُمْ مِنَ الْأَسْرَىٰ إِنْ يَعْلَمِ اللَّهُ فِي قُلُوبِكُمْ خَيْرًا يُؤْتِكُمْ خَيْرًا مِمَّا أُخِذَ مِنْكُمْ وَيَغْفِرْ لَكُمْ ۗ وَاللَّهُ غَفُورٌ رَحِيمٌ

Surah Al - Anfal :70

There is an ayah in Surah al-Anfal that is in the context of War, but the beauty of the Qur’an is such that you can read a verse and it brings a whole new meaning to you than the standard tafsir. Consider this ayah: “…If Allah knows any good in your hearts, He will give you something better than what has been taken from you, and He will forgive you, and Allah is Oft-Forgiving, Most Merciful.” [al-Anfal: 70] 

The Prophet (s) was commanded by Allah to say this to the captives taken in war. But it’s also something that we can say to ourselves whenever a worldly benefit is removed from our hands, because let’s face it: we may not be captives of war, but we are captives of the Dunya and this is why a loss devastates most of us. Our hearts become attached to certain things from this world, and this pollutes the pure nature that the heart was created upon. 

So, to purify the heart, Allah will sometimes remove some things from our possession and we suffer a loss. But He SWT is telling us: if there is goodness in your hearts after this, then there will be no real loss because what Allah gives you in replacement is much better and on top of that He will forgive and show us mercy for what we endure of the loss. So be patient and submit to the Work of Allah SWT, as He Knows all May Allah keep replacing our losses with better things, ameen!

The Prophet SAWS said about our heart: Truly in the body there is a morsel of flesh which, if it be sound, all the body is sound and which, if it be diseased, all of it is diseased. Truly it is the heart. [al-Bukhaari Muslim]

People with sound hearts, according to the Qur'an, have faith in Allah, observe the limits and prohibitions that He has established, and submit to Him fully. In the Islamic sense, there is no other form of a sound heart, for the Qur’an defines a person with a sound heart as someone who constantly brings Allah to mind and feels at peace with His remembrance. The following verse makes this quite clear: “Those who believe and whose hearts find peace in the remembrance of Allah. Only in the remembrance of Allah can the heart find peace.” (Qur’an, 13:28)

Islam has placed great emphasis on purifying the hearts. As a hadith by Prophet Mohammed concerning the day of judgment, says: "Verily Allah does not look to your faces and your wealth but He looks to your heart and to your deeds." 

Those with sound hearts, are also the best people in this world. When the Prophet was once asked "which of the people is best?" he replied: "Everyone who is pure of heart and sincere in speech." 
When they asked him what is meant by a "pure heart", he said: "It is the heart that is pious and pure, with no sin, injustice, rancour or envy in it." 

Ibn Abbas reported: The Prophet, peace and blessings be upon him, said:

رَبِّ اجْعَلْنِي لَكَ شَكَّارًا لَكَ ذَكَّارًا لَكَ رَهَّابًا لَكَ مِطْوَاعًا لَكَ مُخْبِتًا إِلَيْكَ أَوَّاهًا مُنِيبًا رَبِّ تَقَبَّلْ تَوْبَتِي وَاغْسِلْ حَوْبَتِي وَأَجِبْ دَعْوَتِي وَثَبِّتْ حُجَّتِي وَسَدِّدْ لِسَانِي وَاهْدِ قَلْبِي وَاسْلُلْ سَخِيمَةَ صَدْرِي

O Lord, make me grateful to You, remembering of You, fearful of You, obedient to You, humble to You, penitent and repenting. O Lord, accept my repentance, wash away my sin, answer my supplication, establish my proof, direct my tongue, guide my heart, and remove the rancor from my chest.

Source: Sunan al-Tirmidhī 3551, Grade: Sahih