The ones you said would never get mercy: enter Paradise.
Who receives mercy is not ours to swear
The arrogant had sworn that Allah would never show these people mercy. Ibn Abbas said this refers to the people of Al-A'raf. Then Allah decrees for them: enter Paradise, no fear on you, nor will you grieve.
You have written someone off: the cousin who left the deen, the coworker with the past. You are sure how their story ends. The verse is a warning about that certainty.
Some people are obviously beyond Allah's mercy.
I do not get to swear who Allah will have mercy on.
Think of one person you have written off and make a sincere dua for them.