Mana is the foundation of Magic. Although it is possible to design and build decks without mana production, it is extremely difficult. More importantly, the possibilities for mana production define the range of strategic possibilities in Magic. This is why Zvi Mowshowitz once claimed that he began analyzing a format by examining the possibilities inherent in that format’s mana production capacity.
Lands are the building blocks of mana production. While there are many forms of mana production, and while it is possible to build decks without mana producing lands (or even lands at all), mana producing lands are the most basic building block in the game of Magic. They shape and constrain the strategic possibilities in the game.