Apparently, shortly after setting up the Taliban, Mullah Omar opened a sacred reliquary and appeared in public wearing a cloak which had supposedly belonged to the Prophet.
This, to me, was one of the primary motivations behind God's use of the Cross: it discourages (to say the least) the pretence of co-equivalence with Jesus. To those who sought to follow in Jesus' footsteps--in the way that Mullah Omar attempts to do with Muhammad: to assume the Mantle, to be popularly deemed as being on the same plateau, to be perceived as co-equivalent (like John and James mother asking that they be seated on the right and left hand of Jesus in the worldly to come)--to any man so tempted, Jesus said "…let him deny himself and take up his cross daily and follow me." The Cross is what separates the men from the boys…. The Cross puts the story of Jesus on a plateau so elevated above those sorts of petty worldly conceits as to render those conceits beneath notice, to render them spiritually disgraceful, and tread them into the dust. Not just at that time, but two thousand years later: spiritually, going willingly to the Cross puts you way, way, way, way, way up there. Anything else puts you way, way, way, way, way, down here. It would be inconceivable (just to cite the most obvious direct analogy) for the Pope to appear on his balcony at the Vatican with the Shroud of Turin draped over his head.
Essay, "Islam, My Islam", Cerebus 280