An almost theatrical underlining of the fact that nothing very much has changed. Everything He said before, He continues to say. Everything that was true then, continues to be true. And the effect of all of that on the Apostles is the same in each account. Their indecision is resolved.
Aimlessness becomes again a sense of purpose, just as it always had.
The point would seem to be that such is the effect of an encounter with Christ, in any setting, before or after the resurrection. Death just doesn't change things very much. As I say, familiar imagery. By the time this conversation takes place in John's account, the meeting with the risen Christ is pretty well along. The meal is finished, and there is something of the notion that a kind of ease in the presence of Christ has been re-gained.