Allah forbids His believing servants from having Jews and Christians as friends, because they are the enemies of Islam and its people, may Allah curse them. Allah then states that they are friends of each other and He gives a warning threat to those who do this, {And if any among you befriends them, then surely, he is one of them.} Ibn Abi Hatim recorded that 'Umar ordered Abu Musa Al-Ash'ari to send him in writing what he took in and what he spent. Abu Musa then had a Christian secretary, and he was able to fulfill 'Umar's demand. 'Umar liked what he saw and exclaimed, "This person is competent. Would you read in the Masjid a letter that came to us from Ash-Sham?" Abu Musa said, 'He cannot.' 'Umar said, 'Is he not pure?' Abu Musa said, 'No, but he is a Christian.' Abu Musa said, "So 'Umar admonished me and poked my thigh (with his finger), saying, 'Drive him out.' He then recited, {O you who believe! Take not the Jews and the Christians as friends,}" [1] Allah said, {And you see those in whose hearts there is a disease...} A disease of doubt, hesitation and hypocrisy. {they hurry to their friendship,} meaning, they rush to offer them their friendship and allegiances in secret and in public, {saying: "We fear lest some misfortune of a disaster may befall us."} They thus offer this excuse for their friendship and allegiances to the disbelievers, saying that they fear that the disbelievers might defeat the Muslims, so they want to be in favor with the Jews and Christians, to use this favor for their benefit in that eventuality! Allah replied, {Perhaps Allah may bring a victory...} referring to the conquering of Makkah, according to As-Suddi. [2] {or a decision according to His will} requiring the Jews and Christians to pay the Jizyah, as As-Suddi stated, {Then they will become} meaning, the hypocrites who gave their friendship to the Jews and Christians, will become, {for what they have been keeping as a secret in themselves} of allegiances, regretful for their friendship with the Jews and Christians which did not benefit them or protect them from any harm. Rather, it was nothing but harm, as Allah exposed their true reality to His faithful servants in this life, although they tried to conceal it. When the signs that exposed their hypocrisy were compiled against them, their matter became clear to Allah's faithful servants. So the believers were amazed at these hypocrites who pretended to be believers, swearing to their faithfulness, yet their claims were all lies and deceit. This is why Allah said, {And those who believe will say, "Are these the men who swore their strongest oaths by Allah that they were with you?" All that they did has been in vain, and they have become the losers.}

[1] Ibn Abi Hatim 4:1156.
[2] At-Tabari 10:405.