And they ask: "Why a sign is not sent down upon him from his Lord?" You say: "Indeed, Allah is capable to send down a Sign, but indeed most of them are not knowing".
For the disbelievers' question that why are not miracles sent down to the Messenger from his Lord, Messenger is commanded to reply that the miracles are only with the Lord, and he is only a manifest warner as told in verse 29: 50. It is asked through the verse 29: 51 that is not Adhikr sent down to the Messenger enough for the disbelievers as a Miracle. It is told in verse 17: 59 that nothing has prevented the Lord from sending Signs except that the disbelieving and transgressing peoples denied Them.
Today the Arabic Quran reading Fujjar all over the world are reading these verses among mankind. But by hiding and rejecting Adhikr they have become the true disbelievers as explained in verses 4: 150-151. They haven't identified that Adhikr is the Three-Time-Knowledge, Great Sign, Miracle, Lord’s Permission, and Safeguard. Instead of Adhikr, they are teaching and following books written by the pseudo-prophets and hypocrites. The Fujjar will only accept Adhikr when they are being killed by the other people belonging to Messenger's community as told in verse 38: 8. See explanation 2: 211-212; 3: 49-50, and 6: 4-5.