We know in part.  There are things about the spiritual realm that we know.  Some, we know by experience.  This is empirical knowledge.  Some we know by revelation but have not yet appropriated.  Those things that we know are our children’s and ours.  The secret things belong to God, and God will unveil them to us as we grow close to Him.

1 Corinthians 13:9-12 For we know in part, and we prophesy in part.
But when that which is perfect is come, then that which is in part shall be done away.
When I was a child, I spake as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things.
For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known.