not only in spanish. It's the same in all romance languages and many others different ones too, like german, russian, or greek. you'll get used to it after a while. reading helps a lot, it's a lot more useful than learning by heart a list of words. There are exceptions though, like some professions...periodista, artista, for example are masculine :p

The gender applied to objects in Spanish is completely arbitrary, there is nothing at all in a table "mesa" that could indicate us that it can classify as female.

Cause definite article LA is use for female nouns and MESA is one of them! U can't never say EL MESA or LO MESA...is just LA MESA.. ;)

In Spanish nouns have gender (masculine and feminine) and number (singular and plural). The gender depends on the article to be placed before the noun. El, lo, los are defined articles for males. La, las are defined articles for the female gender. Un, unos are indefinite articles for male, una, unas are indefinite articles for the female gender. For example: La mesa, una mesa (female, sing), Las mesas, unas mesas (female, plural).

Hola! Josep: Tu y yo que hablamos Español, debemos aclarar las dudas de las personas sobre nuestro idioma. No te parece?