When this surah came down, everybody was happy — Allah's help had arrived! But one companion, Ibn Abbas, understood something hidden inside it, and it made him sad.
The surah tells the Prophet ﷺ to praise Allah and ask forgiveness. That is what a person does when their work is finished. Ibn Abbas realized it was a gentle sign that the Prophet's mission was complete, and that he would soon leave this world.
He was right. The Prophet ﷺ passed away not long after. That is why this little surah feels both joyful and tender at the same time.