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Answer:
Quote... “And then quite suddenly in another flash, as if lifted by a new strength and resolve, he leaped. No great leap for a man, but a leap in the dark.”
Answer... This quote is saying that Bilbo took a brave leap. The new strength being described here is metaphorical for getting bravery. Not only is Bilbo being brave in this moment, he is stepping outside of his comfort zone. The "flash" means he got a wave of bravery.