The linguistic meaning of fitnah is testing, afflictions, and trials. It is derived from
fitnatul fiddati wa-thahab (the testing of gold and silver when they are melted under
heat to distinguish the pure parts from the impurities). Also, fitnah linguistically
means burning as in the saying of Allaah (subhaanahu wa ta’aalaa) (in the translation
of the meaning):

«(It will be) a Day when they will be tried (i.e. burnt) [yuftanoon] over the Fire!»
Surah ath-Thaariyat (51:13)

As to the legal or Islamic meaning of fitnah, fitnah in essence has the same meaning
as the linguistic definition. That is why the word fitnah came in the Qur’an to mean
trial, testing, and distinguishing. Allaah (subhaanahu wa ta’aalaa) said (in the
translation of the meaning):

«Do people think that they will be left alone because they say: "We believe," and
will not be tested (yuftanoon)?» Surah al-Ankabut (29:2)

Sheikh Belal Assaad explains why there are trials and tribulations.