"And when We cause the people to taste mercy," meaning: well-being and abundance, "they rejoice in it; but if evil afflicts them," meaning: intense punishment, "because of what their hands have put forth, lo! They despair," meaning: they lose hope that any prosperity will reach them thereafter.
﴿وَإِذا أذقنا النَّاس رَحْمَة﴾ يَعْنِي: عَافِيَةً وَسَعَةً ﴿فَرِحُوا بِهَا وَإِن تصبهم سَيِّئَة﴾ يَعْنِي: شدَّة عُقُوبَة ﴿بِمَا قَدَّمَتْ أَيْدِيهِمْ إِذَا هُمْ يقنطون﴾ يَيْأَسُونَ مِنْ أَنْ يُصِيبَهُمْ رَخَاءٌ بَعْدَ