Lessons 1 + 2 discussed the Word of God; how the Bible came to be, who wrote it, what it says, etc. The Word is the ‘what’ of our Christian faith. It contains all the information on which our faith is built and maintained. Next, lesson 3 discussed repentance and faith. They represent the ‘how’ of Christianity. They are the tools through which we access, understand, and utilize God’s Word.
Lesson 4 is about sin, salvation, and forgiveness. The principles learned in this lesson constitute the ‘why’ of Christianity. They explain why a person needs Jesus. They explain the whole reason we believe what we believe. Without an understanding of sin, salvation, and forgiveness – and adherence to the realities of the need for a Savior – the rest of Christian doctrine is useless. That makes this lesson the most important of all.