After the Fall, there is the promise of the Seed to come, who would defeat the Serpent and rule with humanity (Gen. 3:15-16). This promise is traced through the Abrahamic Covenant (Gen. 12:1-3; 15), Davidic Covenant (2 Sam. 7), and New Covenant (Jer. 31:31-34). The Seed is identified as Jesus, the Abrahamic Descendant through whom all the world is blessed (Gal. 3:8; 16). The Davidic King who will rule on earth (Luke 1:32-33). The one through whose blood the New Covenant is inaugurated (Luke 22:20). And finally, the one who will return and rule with humanity over a new creation (Rev. 21-22). This overarching narrative is carried through all of Scripture, along with many other themes and patterns, such as the Melchizedekian priesthood (Gen 14:18; Ps. 110:4; Heb. 5:5-10; 6:19–7:22).
This unity of message and themes requires a single author. Yet, we know the Bible was written over 1500 years, by around 40 authors, in three languages, to different audiences, for various purposes. How do we put this together? The answer is that the Bible has many authors who were "carried along" by the Divine Author (2 Pet. 1:21). Their writings are diverse in their genres, emphases, and purposes, which shows that the authors are not forcing a unity of message. The unity of the message is coming from God.
This unity in diversity is a strong argument that the Bible is God's Word. And if it’s God's Word, then it’s trustworthy. I am so convinced of this that I have given my life to studying and applying God’s Word – you should too.