A slave is like a field that can only grow weeds. A free person is able to bring his entire potential into reality. With hard work he can blossom and bloom. When the final redemption, the final geula comes, all domination in the world, everything which holds us in thrall, will be removed. There will be nothing to prevent us from realizing our full potential.
Nothing remains latent and frustrated.
However, that work was complementary to man's nature. It wasn' t slave labor. It wasn't back-breaking. It was work that man wanted to do. What breaks a person is doing work that he hates, work that goes against the very nature of a person.