The disciples did not recognize Jesus after his resurrection because Jesus appeared in the form of different people. For example, Mary Magdalene mistook him for a gardener (John 20:11-18), he appeared to two disciples on the road to Emmaus as a fellow traveler (Luke 24:13-21), and as a stranger on the shore of the Sea of Galilee to the disciples (John 21:1-13). In each of these cases, the disciples who saw the resurrected Jesus did not recognize him by his physical features, but by what he said and did.
Jesus also appeared as himself after his resurrection. Jesus appeared to Thomas with his wounds from the cross to prove to Thomas by sight that he was resurrected (John 20:26-29). Jesus looked like himself as well when he appeared to the disciples before his ascension (Luke 24:36-51). The disciples were able to touch him so that it proved to them that he was not a ghost or some type of vision.
The disciples learned two important lessons from these appearances after Jesus’ resurrection. First, by seeing Jesus again, the disciples knew he had actually been resurrected. Second, by seeing Jesus take different forms or materialize as different people (just as the angels had done in the Old Testament), they knew he was no longer the man Jesus, but now Jesus had changed into a spirit being.
Other scriptures show that Jesus is no longer an earthly man. The scriptures say that “Now the Lord is that spirit” (2 Corinthians 3:17) and refer to Jesus as “a quickening spirit” (1 Corinthians 15:45). After his resurrection, Jesus also demonstrated the ability to appear within a locked room among the believers (John 20:26-29) and disappear right in front of them (Luke 24:31). This further demonstrated that Jesus was no longer an Earthly man but now with his resurrection changed into a spirit being.