G.N. Lewis invented Lewis structures as a way to describe and understand how electrons surround atoms and also how they hold molecules together. He did this in a non-mathematical, pictorial way in the early 20th century before the birth and subsequent ascent of quantum mechanics. Lewis depicted atoms and their electrons as cubes which could be joined at their edges, vertices, and faces:
By the mid 1920's Lewis had dropped his 3D cubic portrayal of electronic structure; what survives today is rather like a flat 2D projection of those cubes onto a plane. Lewis would have drawn hydrogen cyanide (the molecule that may have killed him) as:
"What is essential is invisible to the eye"
The lasting importance of Lewis's theory is that it provided chemists with a way (albeit simplified) of visualizing the electronic structures of atoms and molecules. That is perhaps why it endures.