I submit to you that, while our conscience gives us knowledge of sin and the handiwork of God in nature is a testament to God’s existence, the only place from which we can learn the gospel (and the surest revelation of the other two) is from the Bible. Therefore, for a Christian, there is no more important task than studying scripture. Crossway has recently published a new book called Understanding Scripture: An Overview of the Bible's Origin, Reliability,and Meaning edited by Wayne Grudem, C. John Collins, and Thomas R. Schreiner which, in my opinion, would be a great help to any Christian seeking to learn more about the Bible. The essays in the book, written by some of the most respected evangelical scholars in the church today (i.e. J.I. Packer and John Piper, to name a few), were originally published in the ESV Study Bible. Collected in this one volume, they serve as an excellent resource for someone who wants to know more about the Bible.
For instance, there are chapters covering how to interpret the Bible (i.e. recognizing the importance of the literary elements of scripture), and how to read the Bible comprehensively (i.e. reading the Bible theologically and prayerfully). However, in my opinion, the strongest essays and probably the most helpful for the average Christian are the chapters that cover the history of Scripture (how it was put together and canonized) and the archeological support for Scripture. In my mind, these are particularly important right now in the church with so many people questioning the truthfulness and reliability of scripture—and that’s just the people in the church not to mention the world outside the church that long ago relegated scripture to little more than fairy tales.
In short, I would recommend this book to any Christian that is serious about their faith and wants to know more about scripture. I could also see this making an excellent book to use for a group Bible study.