Islam is the deen based upon an Arabic Book, which was revealed to the heart of a trusted and trustworthy individual.  Thus, it is no surprise that the reading and learning of Arabic language became the primary goal wherever Islam spread.  The Infallible Qur'an is the uncreated speech of Allah, which is immutable for all ages.  For this reason Muslims have held it absolutely imperative to master the Arabic language.  The Messenger of Allah, may Allah bless him and grant him peace, said as related in the al-Muwwatta of Imam Malik, “I have left for you two matters.  Whoever holds to them will never go astray.  They are the Book of Allah and the Sunna of His Messenger."  Thus, these two sources are the fountainhead of a primal Islam, which is devoid of error and deviation.  These two primal sources are in effect the Muslim's object of reliance in his legal decisions and judgments.  And since the Qur'an was revealed in clear Arabic language and the Sunna of Muhammad has been preserved in Arabic, it is then incumbent upon every Muslim to understand the essentials of the Arabic tongue.
Shaykh Uthman Dan Fuduye said in his renowned Ihya as-Sunna wa'l-Ikhmad al-Bid'a,
"Innovation (bid'a) is that which did not exist during the time of the Prophet, may Allah bless him and grant him peace.  It is as Ibn Abdas Salaam said, 'And included in it (innovation) is that which is obligatory (waajiba) like the prerequisites for understanding of the Book of Allah and the sunna of His Messenger; like grammar (nahw), eloquence (bayaan) and other than these.  This is because the preservation of the shari'a cannot be complete except by means of these sciences.  And that by which an obligation (waajib) is not completed except by it, it too then becomes obligatory."

A portion Shaykh Muhammad's Intro to the translation of the Al-Ajuruumiyyah