In the first century, the Latin that was spoken in the streets of Rome (the Vulgar Latin) was very different from the literary Latin used in books, speeches, and other kinds of formal writing - which is what one learns from today's textbooks. (The same was true for Greek and also for languages of many, if not all, other "civilized" communities of the time; it is still true for some of the languages spoken today.)
In the first century, the Latin that was spoken in the streets of Rome (the Vulgar Latin) was very different from the literary Latin used in books, speeches, and other kinds of formal writing - which is what one learns from today's textbooks. (The same was true for Greek and also for languages of many, if not all, other "civilized" communities of the time; it is still true for some of the languages spoken today.)
[Edit: Sorry for the misplaced comment.]