One of my theories is the usage of the interaction:
"HE is Risen!"
and then people reply "He is Risen Indeed"
Easter morning is one of those rare mornings when a non-churched individual will attend church. And imagine their surprise when someone says 'He is Risen' and the entire room responds with 'HE is Risen INDEED!' as if they practiced it.. perfect unison, strong, loud, joyful.
It's a Christian thing, it's a church thing. And it could make you feel on the outside.
One time my children asked me 'dad why do people do that?'
and this is how I responded:
"Because one day, being a Christian is going to be illegal, and Christian need a way to know who they can trust. If you come across a stranger and you need to know if you can trust them you say 'He is Risen' if they reply 'He is risen indeed!' then you can trust them and go into their house for shelter. But if they reply 'um.. yup, sure whatever dude!' then you know they are not Christians and you can't trust them, and you need to run for your life."
Of course that's not the reason. But its what I said and they knew I was joking.
The real answer seems to be findable on Wikipedia. Apparently it's called a 'Troparion'..
The Paschal greeting, also known as the Easter acclamation, is an Easter custom among Eastern Orthodox, Oriental Orthodox, and Eastern Catholic Christians, as well as among some Roman Catholic and Protestant Christians. Instead of "hello" or its equivalent, one is to greet another person with "Christ is Risen!", and the response is "He is Risen Indeed" (compare Matthew 27:64, Matthew 28:6–7, Mark 16:6, Luke 24:6, Luke 24:34).[1][2]
In some cultures, such as in Russia and Serbia, it is also customary to exchange a triple kiss on the alternating cheeks after the greeting.
Similar responses are also used in the liturgies of other Christian churches, but not so much as general greetings.
