There are a LOT of differences. Classical Latin was the language actually spoken by the Romans. It was their native language. Church Latin, on the other hand, isn't anyone's
… native language. It's Latin used by people after the end of the Roman Empire -- people whose native language isn't Latin, but might be Italian, German, French, Russian, English... you name it. That means that church Latin will be slightly different in different countries, because your native language (whatever it might be) will have a unique impact on your church Latin pronunciation and grammar. Some specific differences: the letter C was always pronounced like "k" in Classical Latin. So the word "centum" (one hundred) sounded like "kentum", for example. But in church Latin, depending on which country you come from, it can be pronounced as "ch" (chentum), "ts" (tsentum) or even "s" (sentum). "ae" in Classical Latin was pronounced like the "ai" at the end of samurai. But in most countries that have church Latin, it's pronounced "ay" (as in "May"). And the grammar is different too. Because no-one has curch Latin as a native language, the word order and grammar they use in church Latin will probably be influenced by the grammar of their native language. And finally, in the many centuries between the "golden age" of Classical Latin and the "golden age" of church Latin, some words changed their meaning or grammar. "Dies", the word for day, is masculine in Classical Latin but feminine in church Latin... and so on. tl;dr: They're two different languages. And many people would say that church Latin isn't really a language at all. (MORE) 
