The apostles in general and the Apostle Paul in particular stressed the importance of studying and teaching sound doctrine. Although there are many important subjects in the Bible, in this book, we have chosen to highlight some that we consider to be very important. I think it is critical that one be as accurate as possible when studying the nature of God, His Son Jesus Christ, the Holy Spirit, and the concept of the Trinity. In addition, it is imperative that the Bible be utilized as the primary source for investigating these doctrines; the Apostle Paul encouraged his spiritual son Timothy to study to show himself approved. Study what? Probably the Old Testament manuscripts and even the letters that had been sent to him. I would like to echo him in saying to all who read this book, study to show yourselves approved because doctrine still matters.