That notation, at best, is begging to be misunderstood. We have become Christ... well no, obviously not. We’re man, he’s God. You need a catechism to explain the catechism!
I could see “the ambassadors of Christ in the image of Christ.” Or something similar. That would be both biblical and accurate. But the formulation given frankly smells of the theological groping of the early centuries which came up with a lot of things that were ALMOST correct.
You need a catechism to explain the catechism!
There is such a book. It is called the “Compendium of the Catechism of the Catholic Church.”
http://www.vatican.va/archive/compendium_ccc/documents/archive_2005_compendium-ccc_en.html