The candle in the famous speech is not a stage prop. The exact meaning of it can be seen in a variety of ways. The idea of the candle being a representation for life or the soul is something that can fit in the context of the description. For Macbeth, hearing the news of his wife's death does not fill him with anything except a sort of existential angst about the nature of being in the world. There is a detachment present, one that feels that life's meaning is vacuous and empty. This is something conveyed throughout the speech. The "tale told by an idiot" or the "signifying nothing" or the "creeps in this petty pace" are all images of an emptiness in life a sense of nothingness present in existence. In this context, the candle can be seen as representative of life, of light, of the soul that might have meant something, but now has no meaning. I don't see it as a direct prop or something tangible on stage, but rather representative of the hope of the intangible, undercut by the reality that Macbeth sees denies one of hope and of promise. I think that in this setting, the candle is symbolic of the potential and possibilities that might exist in life, but one that is "brief" and "out," indicating the illusory nature of what has become of Macbeth's life at this point in the drama.