When I teach the 39 Melochos to teenagers I give the following introduction. The definition of what is allowed or not allowed to do on Shabbos is not defined by what we call work. For example, if your mother asks you to wash the dishes would you consider that 'work'? (I typically get a loud 'yes'); Yet it is permissie to wash dishes on Shabbos! Now, if I put a piece of paper in my pocket and walk out to the street would you call that 'work'? (again a loud 'no'); Yet that is forbidden on Shabbos!
So you see -I continue- that the definition of 'work' that is prohibited on Shabbos is not what we call 'work', rather it is what the Torah defines as forbidden types of actions we mustn't do onShabbos. Now, that is defined by any integral action needed for the construction of the Mishkan (tabernacle).
I give a similar introduction when teaching about the four domains, private and public domains for Shabbos has nothing to do with ownership. A public building (like a Shul) is a private domain, and an open plaza belonging to a private individual could be either a public domain or a Karmilis...
Here are the verses from Torah which motivates such an observance: Shmos 20:10 and 31:15 and 34:21 and 35:3. Bamidbar 15:32. Yermiyahu 17:21&22&24&27. Nechemya 10:32 and 13:15&16&19.