Eternal happiness doing what?
And ask people what gives their lives purpose.
And no heaven no data....Nope, no data no heaven.
And the only plot as far as we know it, is birth, life and death.
Afterlife is speculation....And assuming to have actual knowledge of an afterlife, is fantasy.
Nonetheless... Hypothesising, I would suggest continuity rather that eternity, and the human purpose therein would be to instigate and advance a process of knowledge and material development, to achieve the ultimate principle of knowledge necessary to ensure continuity.
No idling around in a heaven somewhere with stupid grins on our faces, for eternity.