Why is the ability to draw a Lewis structure considered a core chemistry skill?

What is the difference between a single bond and a multiple bond?
Why is the ability to draw a Lewis structure considered a core chemistry skill?
Draw the Lewis structure for hydrogen, the simplest molecule and explain the drawing.
Draw the Lewis structure for PCl3, phosphorus trichloride, the chemical used commercially to prepare insecticides and flame retardants. Explain the drawing.
Draw the Lewis structure for HCN, which has a triple bond. Explain the drawing.
How do you know when you need to add one or more multiple bonds to complete a Lewis structure?

Chemistry: An Introduction to General, Organic, and Biological Chemistry Textbook