Deliberate exaggeration, which no one takes literally, to give emphasis to a feeling or a situation.
In The Idiot
If in that second [...] it happened that he had time to tell himself, clearly and consciously: Yes, for this moment one could give a whole life! then, of course, that moment by itself was worth a whole life.
“For this moment one could give a whole life” exaggerates on purpose. The excess measures the worth of the instant by a whole life and shows the intensity of the light the prince feels before the seizure.