Just like in the beginning of the Surah, Allah the Exalted forbids taking the disbelievers as protecting friends at the end of the Surah, saying,
يَا أَيُّهَا الَّذِينَ امَنُوا لَاا تَتَوَلَّوْا قَوْمًا غَضِبَ اللَّهُ عَلَيْهِمْ
O you who believe!
Take not as friends the people who incurred the wrath of Allah.
referring to the Jews, Christians and the rest of the disbelievers whom Allah became angry with and cursed. Those who deserved being rejected and banished by Him. (Allah says here),
`how can you become their allies, friends and companions, after Allah decided that they earn the despair of receiving any good or delights in the Hereafter'
Allah's statement,
قَدْ يَيِسُوا مِنَ الاْخِرَةِ
..
Surely, they have despaired of the Hereafter,
كَمَا يَيِسَ الْكُفَّارُ مِنْ أَصْحَابِ الْقُبُورِ
just as the disbelievers have despaired of those (buried) in graves.
This has two possible meanings.
First, the disbelievers despair of ever again meeting their relatives buried in graves, because they do not believe in Resurrection or being brought back to life. Therefore, they have no hope that they will meet them again, according to their creed.
Secondly, just as the disbelievers who are buried in graves have lost hope in receiving any kind of goodness (i.e., after seeing the punishment and knowing that Resurrection is true.
Al-A`mash reported from Abu Ad-Duha from Masruq that Ibn Mas`ud said,
كَمَا يَيِسَ الْكُفَّارُ مِنْ أَصْحَابِ الْقُبُورِ
(just as the disbelievers have despaired of those (buried) in graves).
"Just as the disbeliever despairs when he dies and realizes and knows his (evil) recompense."
This is the saying of Mujahid, `Ikrimah, Muqatil, Ibn Zayd, Al-Kalbi and Mansur;
Ibn Jarir preferred this explanation.
This is the end of the Tafsir of Surah Al-Mumtahinah, all praise and thanks be to Allah