The Holy Qur’an...
Thum-ma taliinu juluu-duhum wa quluu-buhum ’ilaa Zikril-laah. Zaa-lika hudal-laahi yahdii bihii man-yashaaa’: wa man-yuzli-lil-laahu famaa lahuu min haad 23.
God bestows from on high the best of all teachings in the shape of a divine writ fully consistent within itself, repeating each statement (of the truth) in manifold forms - (a divine writ) which do shivers the skins of all who of their Sustainer stand in awe: (but) in the end their skins and their hearts do soften at the remembrance of (the grace of) God...... Such is God’s guidance: He guides therewith him that wills (to be guided) - whereas he whom God lets go astray can never find any guide.
The Holy Qur’an was revealed in parts on various occasions during the wide span of twenty-thee (23) years. The greatest proof of the Holy Book being the revealed Word of God is in its uniformity in all its parts conforming to each other and constituting a perfect harmonious whole without the least contradiction or inconsistency anywhere in it, though the circumstances necessitating the revelations, were of varying nature and yet all through the vicissitudes, there is found a perfect uniformity.
As regards God’s guiding whomsoever He pleases and leaving whomsoever He pleases, to stray, refer to Surah an-Nahl, 16:93 , Surah al-Ibrahim, 14:4 and Surah al-Baqarah, 2:26 .