Hi there, I've taught this play for a few years & this is how I've explained this scene in Macbeth. In this soliloquy after his wife's suicide, Macbeth reaises that he has lived his life like a bad actor.He only got one chance on the stage of life and failed through his own ambition and greed.At this stage he realises he's a beaten man and life has become meaningless. He therefore wants to extinguish the candle which brings light to life. He has nowhere to run or hide anymore. Shakespeare is telling us that we only get one chance on the stage of life & it is up to us to do the best we can & to learn from the tragedy of Macbeth.