Why were the two disciples on the road to Emmaus unable to recognize the post-resurrection Christ? What changed that enabled them to see Him?
Here is how it seems to me: prior to breaking bread with them, the disciples observed Christ as an external fact, another person walking on a road with them. When Christ broke break, fact was transformed into gift.
Here is David Bentley Hart:
Christ can now no longer be recognized merely as an available and objective datum, a simple given, but must be received entirely as a donum, as gift, in the breaking of bread, in the offer of fellowship given anew even when the hope of all fellowship seems to have been extinguished.
The Beauty of the Infinite, p. 333