This is a relief for the believers, that is, if you are wounded, do not think that you were the only injured ones, they were injured too, so look at the rest of the verse:

وَتِلْكَ الأيَّامُ نُدَاوِلُهَا بَيْنَ النَّاسِ {And these days [of varying conditions] We alternate among the people}: Allah (swt) did not say (among the believers), but he said: {among people}.

By (days) He does not mean the twenty-four hours, but rather the day on which an event took pace and it is named by it, such as The day of Khandaq, the Day of Badr, and the Day of Uhud.

نُدَاوِلُهَا بَيْنَ النَّاسِ {We alternate among the people}: So victories and defeats, giving and deprivation, health and sickness, poverty and wealth all alternate in a person’s life. Is there anyone who can say that he is unchangeable in any condition? Of course, not because he is living in the world of changes. Today you are young, tomorrow you are old, you were healthy, you became sick, you were strong, you became weak, you were rich, you became poor, you were alive, you became dead, you are changeable, and glory be to Allah the only One Who does not change.

وَلِيَعْلَمَ اللّهُ الَّذِينَ آمَنُواْ {so that Allah may make evident those who believe}: Does not Allah (swt) know everything? In the explanation of the Holy Qur’an, if you take the words literally, you will be greatly mistaken, and you may think that Allah (swt) is alternating among the people and trials come to them so he knows who among them is a believer. Definitely, this is not true, He knows with His eternal revealing knowledge everything, for example, and to Allah belongs the loftiest similitude, we say that the professor who teaches during the whole year and has students, he does not need the exam in order to know who will succeed among his students and who will fail. He (swt) knows each one of them throughout the days of the school year, and through his experience, but he establishes the exam as an argument against the students, Allah (swt) does not hold you accountable for his eternal revealing knowledge, but rather for your work in the exam, and the arena of your exam here is life.

وَيَتَّخِذَ مِنكُمْ شُهَدَاء {and [may] take to Himself from among you martyrs} It is well-known that Allah (swt) honored the martyrs in a way that no one of His creation has been honored after the Prophets, so He (swt) said:

وَلاَ تَحْسَبَنَّ الَّذِينَ قُتِلُواْ فِي سَبِيلِ اللّهِ أَمْوَاتًا بَلْ أَحْيَاء عِندَ رَبِّهِمْ يُرْزَقُونَ

{And never think of those who have been killed in the cause of Allah as dead. Rather, they are alive with their Lord, receiving provision} (Ali-Imran: 169)

وَيَتَّخِذَ مِنكُمْ شُهَدَاء{and [may] take to Himself from among you martyrs}: They bear witness to the truth, for the martyr also bears witness to the truth for which he paid his blood, for Allah (swt) takes to Himself from among you as witnesses to these trials and these conditions, how a person passed them between thankful and patient.

وَاللّهُ لاَ يُحِبُّ الظَّالِمِينَ{and Allah does not like the wrongdoers}: He (swt) likes the doers of good, those who are just, the righteous.