Commanding the people to reflect and ponder upon the Qur'an, and prohibiting them from turning away from it, Allah says,

﴿أَفَلاَ يَتَدَبَّرُونَ الْقُرْءَانَ أَمْ عَلَى قُلُوبٍ أَقْفَالُهَآ ﴾

(Will they not then reflect upon the Qur'an, or are there locks upon their hearts) means, there indeed are locks upon some hearts, firmly closing them so that none of its meanings can reach them. Ibn Jarir recorded from Hisham bin `Urwah, from his father, may Allah be pleased with him, that Allah's Messenger once recited this Ayah,

﴿أَفَلاَ يَتَدَبَّرُونَ الْقُرْءَانَ أَمْ عَلَى قُلُوبٍ أَقْفَالُهَآ ﴾

(Will they not then reflect upon the Qur'an, or are there locks upon their hearts) and a young man from Yemen said, "Indeed, there are locks upon them -- until Allah opens them totally or slightly.'' After that `Umar, may Allah be pleased with him, always liked that young man, and kept that to himself until he became in charge, upon which he utilized him (as a consultant).