Translation:

1. O ye who believe! take not My enemies and yours as friends (or protectors) offering them (your) love even though they have rejected the Truth that has come to you and have (on the contrary) driven out the Prophet and yourselves (from your homes) (simply) because ye believe in Allah your Lord! If ye have come out to strive in My Way and to seek My Good Pleasure (take them not as friends) holding secret converse of love (and friendship) with them: for I know full well all that ye conceal and all that ye reveal. And any of you that does this has strayed from the Straight Path.

Notes (Tafseer)

5409. The immediate occasion for this was a secret letter sent by one Hatib, a Muhajir, from Madinah, to the Pagans at Makkah, in most friendly terms, seeking for their protection on behalf of his children and relatives left behind in Makkah. The letter was intercepted, and he confessed the truth. He was forgiven as he told the truth and his motive did not appear to be heinous, but this instruction was given for future guidance. This was shortly before the conquest of Makkah, but the principle is of universal application. You cannot be on terms of secret intimacy with the enemies of your Faith and people, who are persecuting your Faith and seeking to destroy your Faith and you. You may not do so even for the sake of your relatives as it compromises the life and existence of your whole community.

5410. Such was the position of the Muslim community in Madinah after the Hijrat and before the conquest of Makkah.