The Citizen of the World is perhaps Goldsmith´s best sustained work. It is certainly the best example in English of the essay device so popular at the time in France, which made the essayist a foreign traveler (preferabily Oriental) who wrote letters to his hhhome cuntry describing and critizing the strange customs of the lands through which he passed. The device, initiated in the late seventeenth century by G.P. Marana´s L´Espion Turc and perfected in Montesquieu´s Lettres persanes (1721), throve in France where the critics of established institutions sheltered themselves behind the pretense of being foreigners. Goldsmith drew much inspiration and even many small plagiarized passages.
   In a word the Chinese traveler embodied the pure light of reason, and his mind played effectively over the customs of England and of Christedom in an impartial and at times devasting fashion. To him nothing established had at times devastating fashion. To him nothing established had an absolute validity: in the Orient, as these essayist all loved to remak, polygamy was perfectably respectable; in Christedom the marriage customs were frequently shocking, The excellence of all customs was to be estimated according to human and common-sense standards. If Goldsmith´s "Chinese Letters" are less brilliantly trenchant than the best of his French models, it is in part due to the fact that England was, by definition almost, the land of liberty, and the English unlike the French did not have "God and the king to pull down". Goldsmith is more playfull, more relaxed, more superficial, more  of the literary man, less of the revolutionary.
   Thus the Chinese letters are most useful in giving a picture of Goldsmith´s mind and the temper of his time. From the very begining of his career he had loved to set the qualities of one cuntry over  against the qualities of another. He is a patriot who is sure each nation has its individual and superlative merit. The philosophic mind, he thinks, will attempt to absorb the diverse goods of all nations.
   The title is philosophical rather than political in implication; for Goldsmith, like many another proponent of cosmopolitanism in his day, believed that one should be aware and tolerant of the curious opinions and customs of stange nations.
   In these "Chinese Letters" as well as elsewhere Goldsmith is also typical of his day in his praise of simplicity. He certanily tends to idealize something like an opulent patriarchal society, but even in his picture of "Sweet Auburn" or of the Vicar´s family of Wakwfield, he forgets his dictum that "every age is the same", and shares the predilection of his time for thesimple, though not for the truly primitive.

References:
Routledge & Kegan P. (1967). A Literary History of England, U.K.: Edited by Albert C. Baugh 2nd edition