It's about being born.
"I jumped into the world.
No parachute. Bootless,
falling into enemy territory
into the night (had my eyes closed)."
He was born, naked so he had no boots and his eyes are closed like newborn eyes are apt to be. Enemy territory being the big bad world.
"Slapped me around a bit
but I didn't talk.
Made sure I wouldn't escape.
Sentenced me to life. I guess I deserved it."
Referring to the doctor slapping him on the bottom to make sure he can cry - get the fluid out of his lungs. "Sentenced me to life" simply means that he had no choice and was just brought into the world.
A very clever metaphor, comparing birth to being legislated into a war.