burning like matchsticks in the face of the darkness

I thought it burned and he had to put the cross down after a while. The point seemed to be, "See how much I can do when I put my mind to it. I can pick up this cross and use it as a weapon against you EVEN THOUGH it burns." And note that Spike sees what he has to do as a good thing. Thus a contrast to the earlier burning of his hands in the mottled light, where he is trying to show how tough he can be in evil.

RAS