And Jesus said to them: What are these discourses that you hold one with another as you walk? They stopped, their faces downcast. And the one of them, whose name was Cleophas…
They stopped, their faces downcast
Questioned by that stranger, the travelers to Emmaus stopped, filled with sadness. They were discouraged, only because things did not come out the way they had thought:
… Concerning Jesus of Nazareth, who was a prophet, mighty in work and word before God and all the people. And how our chief priests and princes delivered him to be condemned to death and crucified him. But we hoped that…
In short, they did not understand the meaning of the cross. They had not understood, therefore, the only way through which man can reach Perfect Joy, which always goes arm in arm with Love; and Love, if It is perfect love, always supposes the giving of oneself to the beloved, who in this case is God. Now, in Christ that self-giving is crowned by His death on the Cross in perfect obedience to and total love for the Father and for men. In his actual condition on this earth as a pilgrim on his way to the Heavenly Homeland, man has no other way on which to walk than Jesus Christ (Jn 14:6); that is the giving of his very self and his participation in the cross of the Lord. And there is no other way to find Joy.
Joy departs from men when they seek after themselves instead of self-surrendering to true Love, then Sadness takes its place. The two disciples on their way to Emmaus did not yet know the way to true Joy, hence their sadness and feelings of failure; which is what happens with so many people who think like them.
As they were talking and reasoning with themselves, Jesus himself came up and walked by their side; but their eyes were prevented from recognizing him. (Lk 24: 15-16)
But their eyes were prevented from recognizing him
As one can see, the evangelist says that the disciples are to be blamed for their not being able to recognize the Lord: their eyes were prevented from recognizing him.
The Lord wants to give us His love and intimate friendship. But for Him to do that, He must somehow reveal Himself to us (Jn 14:21), because love is not possible without the knowledge and presence of the beloved person. But one cannot possibly enjoy the presence and love of Jesus Christ if our life is estranged from His; our eyes will fail to recognize Him, and we will not be able to see or hear Him, even though He may be present and calling us (Jn 11:28). For it is imperative to be led by the Spirit of Love if one wants to recognize the Lord.
Perhaps that is why the disciple whom Jesus loved was the first to recognize Him at His appearance by the Sea of Tiberias: They cast the net therefore, and now they were not able to draw it, for the multitude of fishes. That disciple therefore whom Jesus loved said to Peter, ‘It is the Lord.’ 
Nevertheless, it is possible that we are not completely incapable of seeing, for grace can provide us with a certain knowledge and love of the Lord. The Lord then is rather foreseen and sensed, although in a very obscure way (1 Cor 13:12), with an incipient knowledge but which can gradually lead us toward His love, a knowledge and love that grow together and arouse in the soul the hunger and yearning for God.