A reference to an internet meme whose roots trace back to the a webcomic "Toothpaste for Dinner" dated August 30, 2005, titled “Basic Electronic Symbols."
In this comic strip, there were drawings of a Resistor, a Capacitor, and JESUS CHRIST IT'S A LION GET IN THE CAR.
Nowadays the phrase is a typical response to phrases or combinations of phrases like such as:
"I am a lion"
Depending on whether Jesus Christ is present or not, he may render assistance to your current predicament.
Lion: "Rawr. I am a Lion. >:3"
You: "JESUS CHRIST ITS A LION GET IN THE CAR!"
Jesus Christ with a sawed-off shotgun: "I'll handle the lion, you just get in the car."