Imagine with me for a couple of minutes that you are holding a copy of THE DA VINCI CODE in your hands which you have been reading. Suppose that before you reached the page that lies before you (let's call it page Z), you had to first read the page before it (page Y). And before you read that page you had to read the one before it (page X), and so on, going all the way back to the first page. Since the book has a first page, your coming to the current page (Z) requires that you first read only a finite number of pages. More pages could be added to the front of the book to lengthen the time it would take for you to get to page Z. (Hopefully Dan Brown won't read this and get any ideas for a prequel.)
Let us suppose that you are a better than average reader and that it takes only one minute to read each page; and let us supppose that you read non stop until you get to page Z. Then, if there are only ten pages to complete before page Z, it will take you ten minutes to get to page Z. How long will it take if you must first read twenty pages? 20 minutes. How about fifty pages? 50 minutes. A hundred pages? A 100 minutes. Ten thousand pages? You can do the math. The important thing to realize is that in every case, no matter how long the book is, there is always only a finite amount of time that it will take to read it. But let's suppose we add an infinity of pages to the front of this book. When will you get to page Z if you must first read all of those pages? The answer is: Never. So if you find yourself reading page Z after completing all the pages before it, you know you've read only a finite number of pages.
The same sort of thing holds for the series of events making up the total history of the universe. Take some event in the actual history of the universe, like your birth. That event can occur only if a finite number of events must occur first. If an infinite number of events must occur before your birth, then you would never have been born. So, either we are halluncinating regarding the fact of your birth, or only a finite number of events occurred prior to your birth. If only a finite number of events occurred before your birth, then the universe has not always existed but had a beginning. Since we are not hallucinating, the universe must have had a beginning. This poses a problem for the atheist. How does something that begins to exist come into being apart from a creator?
(Thank you to R. Douglas Geivett for his helpful insights on this topic in TO EVERYONE AN ANSWER, edited by Francis Beckwith, William Lane Craig, and J. P. Moreland, chapter 4, 2004, p. 65)