This phrase is from the Godly Play lesson about the Holy Family, written by Jerome W. Berryman. It says that the Christ Child grew up to be a man and died on the cross. That is very sad, but it is also wonderful, in an Easter kind of way. Now... he is everywhere, and in every time.
Nobody invented me [ = God ] – but lots of people discovered me and were quite surprised. They discovered me when they looked round at the world and thought it was really beautiful or really mysterious and wondered where it came from. They discovered me when they were very very quiet on their own and felt a sort of peace and love they hadn’t expected.
I think it sounds very Godly Play!
[Update: the original article, including scans of the letters, can be read here.]