Why has He raised some of us in ranks?

اعوذ بالله من الشيطن الرجيم

Surah 6. Al-Anaam, Verse 165:

وَهُوَ الَّذِي جَعَلَكُمْ خَلَائِفَ الْأَرْضِ وَرَفَعَ بَعْضَكُمْ فَوْقَ بَعْضٍ دَرَجَاتٍ لِّيَبْلُوَكُمْ فِي مَا آتَاكُمْ إِنَّ رَبَّكَ سَرِيعُ الْعِقَابِ وَإِنَّهُ لَغَفُورٌ رَّحِيمٌ

Translation:

And it is He Who has made you generations coming after generations, replacing each other on the earth. And He has raised you in ranks, some above others that He may try you in that which He has bestowed on you. Surely your Lord is Swift in retribution, and certainly He is Oft-Forgiving, Most Merciful.

Allah's وصية

اعوذ بالله من الشيطن الرجيم

Surah 6. Al-Anaam, Verse 152:

وَلَا تَقْرَبُوا مَالَ الْيَتِيمِ إِلَّا بِالَّتِي هِيَ أَحْسَنُ حَتَّىٰ يَبْلُغَ أَشُدَّهُ وَأَوْفُوا الْكَيْلَ وَالْمِيزَانَ بِالْقِسْطِ لَا نُكَلِّفُ نَفْسًا إِلَّا وُسْعَهَا وَإِذَا قُلْتُمْ فَاعْدِلُوا وَلَوْ كَانَ ذَا قُرْبَىٰ وَبِعَهْدِ اللَّهِ أَوْفُوا ذَٰلِكُمْ وَصَّاكُم بِهِ لَعَلَّكُمْ تَذَكَّرُونَ

Translation:

"And come not near to the orphan's property, except to improve it, until he (or she) attains the age of full strength; and give full measure and full weight with justice. We burden not any person, but that which he can bear. And whenever you give your word (i.e. judge between men or give evidence, etc.), say the truth even if a near relative is concerned, and fulfill the Covenant of Allah, This He commands you, that you may remember.