The Heart of the Bible by John MacArthur
This is probably the best summary (quick) understanding of the important scripture references every Christian should know.
MacArthur gives 52 key verses and a brief explanation of each. The idea of the book is for the reader to read, understand, and think about one piece of scripture a week for the entire year.
The passages are grouped together in chapters to help the reader focus on one aspect of Christianity for several weeks before moving on to the next topic.
I would strongly recommend this book to a new or growing Christian. This would also be a good book for a more mature Christian looking to deepen or strengthen their faith as well.