The people of Mecca may, for a time, have been stirred by the constant 
reiteration of an impending local danger but, as time passed by and no calamity 
came to them, they passed from curiosity to incredulity. They challenged 
Muhammad's message, derided his denunciations and demanded miraculous signs of 
his authority.
They said:
By no means will we believe in thee till thou cause a fountain to gush forth  
for us from the earth,
 
Or till thou have a garden of palm-trees and grapes, and thou cause forth  
gushing rivers to gush forth in our midst;
 
  
Or thou make the heaven to fall on us, as thou hast given out, in pieces; or  
thou bring God and the angels to vouch for thee. Sura Al-Isra (xvii), 92-5.
 
The unbelievers say, ' Why hath not a sign been given him by his Lord.' Sura  
Ar-Ra'd (xiii) 8.
 
Muhammad had to acknowledge that he had no such credentials, but he brought 
revelations to show that the absence of this power was part of God's purpose in 
dealing with these rebellious people of Mecca.
Thus, in order to show that what he deemed mere idle curiosity could not be 
gratified, we have :
We will not send down the angels without due cause. Suratu Al-Hijr (xv) 8.
If they would not believe from the example of those who had gone before, if 
they now deliberately rejected the warning and the warner, then nothing