Surah al-Kafirun is the 109th surah of the Quran. It was revealed in Mecca, when Muslims were being persecuted by the polytheists of Mecca.
This article provides the full Arabic text, French translation and tafsir of Surah al-Kafirun.
First, here is the complete Arabic text of Surah al-Kafirun:

Translation
Say: « O disbelievers!
I do not worship what you worship.
And you are not worshippers of what I worship.
I am not a worshipper of what you worship.
And you are not worshippers of what I worship.
« To you your religion, and to me my religion. »
Tafsir
During his prayers, the Prophet Muhammad (peace and blessings be upon him) often recited Surah al-Kafirun along with Surah al-Ikhlas. As such, Surah al-Kafirun and Surah al-Ikhlas are collectively known as al-Ikhlasayn.
The first verse, « Say, ‘O disbelievers!’ » can refer to all disbelievers throughout the world, although it was specifically revealed to the Messenger of Allah (peace and blessings be upon him) when the pagan Quraysh asked him to worship their idols for a year, and in return, they would worship Allah the following year. At that time, Surah al-Kafirun was revealed to reject these false idols and polytheism. This surah is therefore a declaration of liberation from Shirk (associating partners with Allah) and a purification of the hearts of all believers.
The second through fifth verses of this surah inform the disbelievers that we worship no entity other than Allah, the One and Only Supreme Being. As Muslims, we worship only Allah and do not associate any partners or demigods with Him.

Finally, the sixth verse of Surah al-Kafirun is, according to Imam ash-Shafi’i (RA), a confirmation of Islamic monotheism. Essentially, Islam is the ultimate monotheistic faith because it is unparalleled in its connection to Allah. Furthermore, the last verse reaffirms the difference between belief and disbelief: « For you is your religion, and for me is my religion. »
Featured image: Quranic inscriptions on the wall of Bara Gumbad Masjid, Delhi (India) | Photo from wikimediaCommons