Einstein's thought of a person under free-fall and when suspended in free space with no forces acting, will feel the same way. On Walter lewin's lecture on free fall he told free fall is when only gravity force is acting on a body (Newtonian Mechanics).
How is these two thoughts connect, how both the conditions are same, one has a net force acting other has no net force. If we have to design a component/machine to work under these conditions, do we have to consider any forces, if so, which force.
Edit: Improved understanding There is no force of gravity, when a body is in free space, the space-time is flat, in a gravity field its curved, a body placed in both will follow a geodesic path if no external force is acting. This motion of the body in a geodesic path on a curved spacetime is manifested as a body under constant acceleration.