Why was land the most important gift a lord could give a vassal?

Because land was like gold nowadays if u had a large piece of land u were considered to be high class

This is known as a society system. America is nothing like this. An example of this today is called the caste system in India. 
A vassal could also be known as a slave. 

Answer;

When land is given to a vassal, he no longer becomes a vassal, but a lord. 
This is a huge change in his society standing.

Towns and small farms are usually for land, lakes, rivers, and seas.they also produce other food, like crops.it's also where animals are, where we get our meat.large plantations normally have forests, where crops are grown for sale. (similar to farms)plantations have larger fields of crops.our wine, sugar canes, and fruits come from plantations.