This seemingly solid body that sits at my seemingly solid desk is a swirling cloud of electrons and other infinitesimally small particles. In one atom, the spaces between nucleus and electrons are like the spaces between sun and planets. We are indeed mostly space. This exercise asks that you imagine that reality as reality.
Imagine your body as a mesh of fine charged wire, an energy grid, or a cloud of electrons.
Rather than resisting oncoming energy, let it pass through you as easily as the wind blowing through a wire fence.