Great question, and great comments! This is the most comprehensive answer I've found anywhere:
* Draw Close to Jehovah book, chapter 18, pp. 179-187 Wisdom in “the Word of God” *
Why a Written Word?
3 Some may wonder, ‘Why did Jehovah not use a more dramatic method—say, a voice from heaven—to communicate with humans?’ In fact, Jehovah did at times speak from heaven by means of angelic representatives. He did so, for example, when he gave the Law to Israel. (Galatians 3:19) The voice from heaven was awe-inspiring—so much so that the terrified Israelites asked that Jehovah not speak with them in this manner but that he communicate through Moses. (Exodus 20:18-20) The Law, consisting of some 600 statutes, was thus transmitted to Moses orally, word-for-word.
4 What, though, if that Law had never been put in writing? Would Moses have been able to remember the precise wording of that detailed code and to convey it flawlessly to the rest of the nation? What about later generations? Would they have had to rely solely on word of mouth? That would hardly have been a reliable method of handing down God’s laws. Imagine what would happen if you were to transmit a story to a long line of people by telling it to the first person and then having it relayed from one to another down the line. What the person at the end of the line heard would likely differ considerably from the original. The words of God’s Law were in no such danger.
5 Jehovah wisely chose to have his words put in writing. He instructed Moses: “Write down for yourself these words, because it is in accordance with these words that I do conclude a covenant with you and Israel.” (Exodus 34:27) So began the era of Bible writing, in 1513 B.C.E. Over the next 1,610 years, Jehovah “spoke on many occasions and in many ways” to some 40 human writers who then penned the Bible. (Hebrews 1:1) Along the way, devoted copyists took meticulous care to produce accurate copies so as to preserve the Scriptures.—Ezra 7:6; Psalm 45:1.
6 Jehovah has truly blessed us by communicating with us in writing. Have you ever received a letter that was so dear to you—perhaps because it offered needed comfort—that you saved it and read it again and again? So it is with Jehovah’s “letter” to us. Because Jehovah put his words in written form, we are able to read them regularly and to meditate on what they say. (Psalm 1:2) We can receive “the comfort from the Scriptures” whenever we need it.—Romans 15:4.
Why Human Writers?
7 In his wisdom, Jehovah used humans to pen his Word. Consider this: If Jehovah had used angels to record the Bible, would it have the same appeal? Granted, angels could have portrayed Jehovah from their lofty viewpoint, expressed their own devotion to him, and reported on faithful human servants of God. But would we really have been able to identify with the perspective of perfect spirit creatures, whose knowledge, experience, and strength are far superior to our own?—Hebrews 2:6, 7.
8 Through his use of human writers, Jehovah provided just what we need—a record that is “inspired of God” yet retains the human element. (2 Timothy 3:16) How did he achieve this? In many cases, he evidently allowed the writers to use their own mental faculties in selecting “the delightful words and the writing of correct words of truth.” (Ecclesiastes 12:10, 11) This explains the Bible’s diversity of style; the writings reflect the background and personality of the individual writers. Yet, these men “spoke from God as they were borne along by holy spirit.” (2 Peter 1:21) Hence, the end product truly is “the word of God.”—1 Thessalonians 2:13.
9 The use of human penmen gives the Bible tremendous warmth and appeal. Its writers were men with feelings like ours. Being imperfect, they faced trials and pressures similar to our own. In some cases, Jehovah’s spirit inspired them to write about their own feelings and struggles. (2 Corinthians 12:7-10) So they penned words in the first person, words that no angel could have expressed.
10 Take, for example, King David of Israel. After he had committed some serious sins, David composed a psalm in which he poured out his heart, begging for God’s forgiveness. He wrote: “Cleanse me even from my sin. For my transgressions I myself know, and my sin is in front of me constantly. Look! With error I was brought forth with birth pains, and in sin my mother conceived me. Do not throw me away from before your face; and your holy spirit O do not take away from me. The sacrifices to God are a broken spirit; a heart broken and crushed, O God, you will not despise.” (Psalm 51:2, 3, 5, 11, 17) Can you not feel the writer’s anguish? Who but an imperfect human could express such heartfelt sentiments?
Why a Book About People?
11 There is something else that contributes to the Bible’s appeal. To a large extent, it is a book about people—real people—those serving God and those not serving him. We read about their experiences, hardships, and joys. We see the outcome of their choices in life. Such accounts were included “for our instruction.” (Romans 15:4) Through these true-life portrayals, Jehovah teaches in ways that touch our heart. Consider some examples.
12 The Bible tells about unfaithful, even wicked, humans and what befell them. In these accounts, undesirable qualities are seen in action, making them easier for us to comprehend. For instance, what command against disloyalty could be more powerful than the living example of this quality in Judas as he carried out his traitorous plot against Jesus? (Matthew 26:14-16, 46-50; 27:3-10) Accounts such as this reach our heart more effectively, helping us to recognize and reject loathsome traits.
13 The Bible also describes many faithful servants of God. We read about their devotion and loyalty. We see living illustrations of the qualities we need to cultivate in order to draw close to God. Take faith, for example. The Bible defines faith and tells us how essential it is if we would please God. (Hebrews 11:1, 6) But the Bible also contains vivid examples of faith in action. Think about the faith Abraham showed when he attempted to offer up Isaac. (Genesis, chapter 22; Hebrews 11:17-19) Through such accounts, the word “faith” takes on added meaning and becomes easier to grasp. How wise that Jehovah not only exhorts us to cultivate desirable qualities but also provides examples of them in action!
14 The real-life accounts found in the Bible often teach us something about the kind of person Jehovah is. Consider what we read about a woman whom Jesus observed in the temple. While seated near the treasury chests, Jesus was watching as the people dropped in their contributions. Many rich ones came, giving “out of their surplus.” But Jesus’ gaze became fixed on a lowly widow. Her gift consisted of “two small coins, which have very little value.” It was the last bit of money she had. Jesus, who perfectly reflected Jehovah’s mind on matters, noted: “This poor widow dropped in more than all those dropping money into the treasury chests.” According to those words, she put in more than all the others combined.—Mark 12:41-44; Luke 21:1-4; John 8:28.
15 Is it not significant that of all the people who came to the temple that day, this widow was singled out and mentioned in the Bible? Through this example, Jehovah teaches us that he is an appreciative God. He is pleased to accept our whole-souled gifts, no matter how they compare with what others are able to give. Jehovah could hardly have found a better way to teach us this heartwarming truth!
What the Bible Does Not Contain
16 When you write a letter to a loved one, there is only so much you can include. So you use discretion in choosing what to write. Likewise, Jehovah chose to mention certain individuals and events in his Word. But in these descriptive accounts, the Bible does not always spell out all the details. (John 21:25) For example, when the Bible tells of God’s judgment, the information provided may not answer our every question. Jehovah’s wisdom is seen even in what he chose to leave out of his Word. How so?
17 The way in which the Bible is written serves to test what is in our heart. Hebrews 4:12 says: “The word [or, message] of God is alive and exerts power and is sharper than any two-edged sword and pierces even to the dividing of soul and spirit . . . and is able to discern thoughts and intentions of the heart.” The Bible’s message pierces deep, revealing our true thinking and motives. Those who read it with a critical heart are often stumbled by accounts that do not contain enough information to satisfy them. Such ones may even question whether Jehovah really is loving, wise, and just.
18 In contrast, when we make a careful study of the Bible with a sincere heart, we come to see Jehovah in the context in which the Bible as a whole presents him. Hence, we are not disturbed if a particular account raises some questions to which we cannot find immediate answers. To illustrate: When piecing together a large puzzle, perhaps we cannot at first find a particular piece or we cannot see how a certain piece fits in. Yet, we may have assembled enough of the pieces to grasp what the complete picture must look like. Similarly, when we study the Bible, little by little we learn about the kind of God Jehovah is, and a definite picture emerges. Even if we cannot at first understand a certain account or see how it fits in with God’s personality, our study of the Bible has already taught us more than enough about Jehovah to enable us to see that he is unfailingly a loving, fair, and just God.
19 To comprehend God’s Word, then, we must read and study it with a sincere heart and an open mind. Is this not evidence of Jehovah’s great wisdom? Clever humans can write books that only “wise and intellectual ones” can grasp. But to author a book that can be understood only by those having the right heart motivation—that takes the wisdom of God!—Matthew 11:25.