Those who break Allah's covenant after ratifying it, and sever what Allah has ordered to be joined and do mischief on earth, it is they who are the losers.
These are the characteristics of the disbelievers and they contradict the qualities of the believers.
Similarly, Allah said in Surah Ar-Ra`d,
أَفَمَن يَعْلَمُ أَنَّمَأ أُنزِلَ إِلَيْكَ مِن رَبِّكَ الْحَقُّ كَمَنْ هُوَ أَعْمَى إِنَّمَا يَتَذَكَّرُ أُوْلُواْ الَالْبَـبِ
الَّذِينَ يُوفُونَ بِعَهْدِ اللَّهِ وَلَا يِنقُضُونَ الْمِيثَـقَ
وَالَّذِينَ يَصِلُونَ مَأ أَمَرَ اللَّهُ بِهِ أَن يُوصَلَ وَيَخْشَوْنَ رَبَّهُمْ وَيَخَافُونَ سُوءَ الحِسَابِ
Shall he then, who knows that what has been revealed unto you (O Muhammad) from your Lord is the truth, be like him who is blind! But it is only the men of understanding that pay heed.
Those who fulfill the covenant of Allah and break not the Mithaq (bond, treaty, covenant).
And those who join that which Allah has commanded to be joined (i.e. they are good to their relatives and do not sever the bond of kinship), and fear their Lord, and dread the terrible reckoning. (13;19-21)) until,
وَالَّذِينَ يَنقُضُونَ عَهْدَ اللَّهِ مِن بَعْدِ مِيثَـقِهِ وَيَقْطَعُونَ مَأ أَمَرَ اللَّهُ بِهِ أَن يُوصَلَ وَيُفْسِدُونَ فِى الاٌّرْضِ أُوْلَـيِكَ لَهُمُ اللَّعْنَةُ وَلَهُمْ سُوءُ الدَّارِ
And those who break the covenant of Allah, after its ratification, and sever that which Allah has commanded to be joined (i.e. they sever the bond of kinship and are not good to their relatives), and work mischief in the land, on them is the curse (i.e. they will be far away from Allah's mercy), and for them is the unhappy (evil) home (i.e. Hell). (13;25)
The covenant that these deviant people broke is Allah's covenant with His creation, that is, to obey Him and avoid the sins that He prohibited. This covenant was reiterated in Allah's Books and by the words of His Messengers. Ignoring this covenant constitutes breaking it.
It was said that the Ayah (2;27) is about the disbelievers and the hypocrites among the People of the Book. In this case, the covenant that they broke is the pledge that Allah took from them in the Tawrah to follow Muhammad when he is sent as a Prophet, and to believe in him, and in what he was sent with. Breaking Allah's covenant in this case occurred when the People of the Book rejected the Prophet after they knew the truth about him, and they hid this truth from people, even though they swore to Allah that they would do otherwise. Allah informed us that they threw the covenant behind their backs and sold it for a miserable price.
It was also reported that the Ayah (2;27) refers to all disbelievers, idol worshippers and hypocrites. Allah took their pledge to believe in His Oneness, showing them the signs that testify to His Lordship. He also took a covenant from them to obey His commands and refrain from His prohibitions, knowing that His Messengers would bring proofs and miracles that none among the creation could ever produce. These miracles testified to the truth of Allah's Messengers. The covenant was broken when the disbelievers denied what was proven to them to be authentic and rejected Allah's Prophets and Books, although they knew that they were the truth.
This Tafsir was reported from Muqatil bin Hayyan, and it is very good. It is also the view that Az-Zamakhshari held.
Allah's statement next,
وَيَقْطَعُونَ مَا أَمَرَ اللَّهُ بِهِ أَن يُوصَلَ
And sever what Allah has ordered to be joined,
is in reference to keeping the relations with the relatives, as Qatadah asserted.
This Ayah is similar to Allah's statement,
فَهَلْ عَسَيْتُمْ إِن تَوَلَّيْتُمْ أَن تُفْسِدُواْ فِى الاٌّرْضِ وَتُقَطِّعُواْ أَرْحَامَكُمْ
Would you then, if you were given the authority, do mischief in the land, and sever your ties of kinship. (47;22)
Ibn Jarir At-Tabari preferred this opinion.
However, it has been said that the meaning of the Ayah (2;27) here is more general. Hence, everything that Allah has commanded to nurture, and the people severed, is included in its meaning.
The Meaning of `Loss
Muqatil bin Hayyan commented on Allah's statement,
أُولَـيِكَ هُمُ الْخَاسِرُون
(It is they who are the losers),
"In the Hereafter."
Similarly, Allah said,
أُوْلَـيِكَ لَهُمُ اللَّعْنَةُ وَلَهُمْ سُوءُ الدَّارِ
On them is the curse (i.e. they will be far away from Allah's mercy), and for them is the unhappy (evil) home (i.e. Hell). (13;25)
Also, Ad-Dahhak said that Ibn Abbas said,
"Every characteristic that Allah describes those other than the people of Islam - such as being losers - then it refers to disbelief. However, when they are attributed to the people of Islam, then these terms refer to sin."
Ibn Jarir commented on Allah's statement,
أُولَـيِكَ هُمُ الْخَاسِرُون
(It is they who are the losers),
"Losers is plural for loser, this word refers to whoever decreased his own share of Allah's mercy by disobeying Him, just as the merchant loses in his trade by sustaining capital loss. Such is the case with the hypocrite and the disbeliever who lose their share of the mercy that Allah has in store for His servants on the Day of Resurrection. And that is when the disbeliever and the hypocrite most desperately need Allah's mercy.