Allah, Glorified and Praised, addresses the believers and the disbelievers

 I take refuge with Allaah from the accursed devil. 
بِسْمِ اللَّهِ الرَّحْمَـنِ الرَّحِيمِ
  Bismillah-ir-Rahman-ir-Raheem: In the name of Allah, the Compassionate, the Merciful. 
  Welcome to my blog and praise the Magnificent Lord as you enter: Allahu Akbar: Allah is the Greatest .
  May the Peace and Blessing of Allah Azza wa Jal, our Lord Glorified and Praised be He, be upon our beloved  Prophet, his Family, and Companions.
Allah, Glorified and Praised, addresses the believers and the disbelievers.
يَـأَيُّهَا الَّذِينَ ءَامَنُواْ ءَامِنُواْ بِاللَّهِ وَرَسُولِهِ وَالْكِتَـبِ الَّذِى نَزَّلَ عَلَى رَسُولِهِ وَالْكِتَـبِ الَّذِى أَنَزلَ مِن قَبْلُ وَمَن يَكْفُرْ بِاللَّهِ وَمَلَـئِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ وَالْيَوْمِ الاٌّخِرِ فَقَدْ ضَلَّ ضَلَـلاً بَعِيداً
(136. O you who believe! Believe in Allah, and His Messenger, and the Book (the Qur’an) which He has sent down to His Messenger, and the Scripture which He sent down to those before; and whosoever disbelieves in Allah, His Angels, His Books, His Messengers, and the Last Day, then indeed he has strayed far away.)
Surah 2 An Nisaa Verse 136
Tafsir Ibn Kathir
Allah commands His faithful servants to adhere to all the elements of faith, its branches, pillars and cornerstones. This is not stated as mere redundancy, but from the view of completing faith and the continual maintenence of it. For instance, the believer proclaims in every prayer,
(Guide us to the straight way.) which means, make us aware of the straight path and increase us in guidance and strengthen us on it. In this Ayah [4:136], Allah commands the believers to believe in Him and in His Messenger, just as He said elsewhere,
(O you who believe! Have Taqwa of Allah, and believe in His Messenger, ). Allah’s statement,
(and the Book which He has sent down to His Messenger,) refers to the Qur’an, while,
(and the Scripture which He sent down to those before (him);) refers to the previously revealed divine Books. Allah then said,
(and whosoever disbelieves in Allah, His Angels, His Books, His Messengers, and the Last Day, then indeed he has strayed far away.) meaning, he will have deviated from the correct guidance and strayed far away from its path.