• Verb: have an existence, be extant; example: "Is there a God?"
• Verb: support oneself; examples: "he could barely exist on such a low wage", "Can you live on $2000 a month in New York City?", "Many people in the world have to subsist on $1 a day"
In order to exist just once in the world, it is necessary never again to exist.
It is incomprehensible that God should exist, and it is incomprehensible that he should not exist.