Girls names in Polish - why do they end in "a"?

Why do al girls names in Polish end in "A"? I asked this question today and I was told its because its the way the language works. Can anyone elaborate on this?

Because that's the way it is.
Most feminine objects end with an "a" also, example:
ta kapusta
ta sukienka
ta woda
Masculine objects end on any letter they want:
ten samochód
ten but
ten talerz
Then there are these neutral dudes that end with an "o":
to krzesło
to masło
to piwo

any consonant they want, I'd add. There are some masculine nouns ending in vowels, like "poeta" for example, but these are of obviously foreign origin, or meant to be funny - like "wierszokleta" for example ;-)

also...kolega,mężczyna,dentysta,specjalista :)

kolega, dentysta, specjalista are all non-Polish in origin.
Mężczyzna, on the other hand, is rather strange in this respect, as it is a Slavonic word, and its meaning is 100% masculine, yet it ends in -a... Weird. Hadn't thought of it earlier. ;-)

Kuba (Jakub, James), i think is the only Masculine name that ends with 'a'.
and it's my name btw.

In Polish "a" is feminine gender marker (in singular nominative) just like "s" in English is a plural marker for nouns. And female names in Polish are always in feminine grammatical gender.

Thank you so much for a consise and understandable reply. However what does the above mean exactly?

I'll explain you on examples:

a cat - singular
cats - plural
a child - singular
children - plural

When you talk about one thing, it's singular, if more than one, it's plural..

Nominative case is the form of the noun that is used when this noun is the subject of the sentence. You have something similar in English pronouns, e.g. you've got the pronoun "he" in three forms: he, him, his. 'He' is the subjective case form, 'his' is genitive or possesive case form and 'him' is objective case form. Now, each Polish noun, nominal pronoun or adjectives has 7 forms (called cases). Nominal case form is the basic form of the word, so when you ask someone about the name, they will tell it to you in this case.

Switezianka,

That was an exquisite explanation. Thank you... :')