Allah said:
"And We have made some of you [people] as trial for others, will you have patience?" (25:20)People to whom the Messengers were sent were a trial for the Messengers themself, to test their patience, to see if they could bear the difficulty and rejection caused by these people while conveying the message of Allah.
The Messengers were a trial for their people also, to know who was gonna obey them and testify to the truth or simply disbelieve and reject them.
We will all be tested, from Adam to the last human on this earth.
Allah said:
"Do the people think they will be left to say, "We believe" and they will not be tried?" (29:2)Days will be hard and we'll have to keep enduring and days will be easy and we'll have to be thankful for what the Lord bestowed upon us. Because SubhanAllah, even in our good days, it's quite easy to become arrogant and think that every good things that we have is because of us.
And people will also be put into our life to test us. To test our faith, to test our patience, our commitment, our sincerity and so on.
We need to keep one thing in mind: our goal is Jannah. The way we treated people in this life will either testity for us or against us on the day of judgment. The way we bore patience will also testify for us or against us. Our gratefulness or arrogance will testify for us or against us. All those things will weight on the balance of the Akhira. We really need to be mindful of this.