Allaah (The Most High) said:

وَجَعَلْنَا بَعْضَكُمْ لِبَعْضٍ فِتْنَةً أَتَصْبِرُونَ

And We have made some of you as a trial for others: will you have patience? [Soorah Al-Furqaan]

Imaam Ibnul Qayyim (rahimahullaah) said:

This is universal amongst all the creation- they are put to trial by one another. Those whom the Messengers are sent to are a trial for the Messengers—in calling them to the truth, exercising patience in facing their harm and bearing the difficulty in conveying the Message of their Lord. And the Messengers are a trial for those whom they have been sent to, as to whether they will obey and aid them, and testify to the truth of that which they have been sent with; or whether they will disbelieve, reject and fight them.

The ignorant people are a trial for the scholars, as to whether they will teach and advise them, whilst exercising patience in teaching, advising, guiding them and been constant in that.

And the scholars are a trial for the ignorant people, as to whether they will obey them and follow their example.

The subjects are a trial for the kings and the kings are a trial for the subjects.

The poor people are a trial for the rich people and the rich people are a trial for the poor people.

The weak people are a trial for the strong people and the strong people are a trial for the weak people.

The leaders are put to trial by those who follow them and those who follow are put to trial by way of the leaders.

The slave master is put to trial by way of his slaves and the slaves are put to trial by way of the slave master.

A man is put to trial by way of his wife and his wife is put to trial by way of him.

The men are put to trial by way of women and women are put to trial by way of men.

The believers are put to trial by way of the disbelievers and the disbelievers are put to trial by way of the believers.

Those who enjoin good and forbid evil are put to trial by way of those whom they command good and forbid from evil, and those commanded with good and forbidden from evil are put to trial by way of those who command them with good and forbid them from evil…..

[Source: Ighaathatul Luhfaan: 2/170-172]