Luke 24:13-16
13 Now that same day two of them were going to a village called Emmaus, about seven miles from Jerusalem. 14 They were talking with each other about everything that had happened. 15 As they talked and discussed these things with each other, Jesus himself came up and walked along with them; 16 but they were kept from recognizing him.
(from New International Version)

The question behind the mode of appearance seems to be what Jesus' purpose was in meeting and talking with the two disciples. If his purpose had been to inspire awe and provoke fear or worship, he could have appeared in recognizable form (as in Matt. 28:8-10), but he seemed to have a desire to have a real dialogue with them, and get them to really think about the meaning of the scriptures and the events that had occurred. Sometimes a dawning realization with pieces falling into place and connections being seen is better than an "epiphany". The story points up the miraculous of course, but it highlights the intact personality and character of the resurrected Lord, interacting with two of his disciples in a familiar and constructive way, which he could only do "in disguise" at that point.