The word Scripture simply means writings. Of course the only writings that are fully the words of God are those found in the Torah, Prophets and Writings of the Old and New Testaments. But the word Scripture only tells us they are writings. The more I study the structure of Scripture the more I realize that the shape of the book is an apologetic for the importance of the book. In fact, the third section of the canon in the Old Testament is called the Writings. Actually, we might as well call them the Scriptures. Thus just as the Torah (Deuteronomy) is a name we apply to the first section, so the Writings is a name we apply to all the Bible.
The shape of Scripture is an apologetic for the importance of Scripture study. You can see this clearly at the seams of the three sections: Deut 34, Josh 1, Malachi 4, and Psalm 1. It is the reason we are so passionate about The Book.
In any case, the Writings are in conversation (though not in an oral but written form) with the rest of Scripture. The Prophets interpret Torah for a new generation. The Writings are reflections on the Torah and Prophets. Likewise in the New Testament, the New Testament writings are interpreting the significance of the death and resurrection of Christ (Gospels, NT Torah) and the giving of the Spirit on Pentecost (Acts, NT Prophets).
And the Writings are in conversation with each other. The first three: Psalms, Job, and Proverbs are all accented as poetry for chanting in Hebrew. The next five were chanted at festivals during the year: Ruth, Song of Songs, Qoheleth (Ecclesiastes), Lamentations, and Esther. And then the last three are Daniel, Ezra-Nehemiah, and Chronicles. The ones chanted at festivals form a chiasm — Ruth the heroine, Song of Songs is erotic poetry, Ecclesiastes in the middle, Lamentations is sad poetry, and Esther the heroine. Thus with three before and three after these five the whole of the Writings makes a chiasm.
The sections within the Writings are stitched together when we realize that Proverbs ends with the poem about the ideal wife (Prov 31:10) and Boaz says that everyone knows Ruth would be the ideal wife (Ruth 3:11). In Hebrew the phrase is identical. Song of Songs gives us another example of the ideal wife, as does Esther parallel to Ruth. Also Esther in many ways is a female Daniel, which bridges those two books together. But already you should be able to see that the Writings are in conversation with one another.
One common literary form in the Writings is the alphabetic acrostic poem. One reason that you would do an alphabetic acrostic is to speak comprehensively. Thus the alphabetic acrostic par excellence is Psalm 119, with eight lines for each letter of the Hebrew alphabet (making it also the longest chapter in the Scriptures). The book of Lamentations consists of six alphabetic acrostics. The poem about the ideal wife in Prov 31:10ff is another example. It is a comprehensive description of the ideal wife from A to Z (for the English alphabetic equivalent). This is in conversation, as Longman notes in his Proverbs commentary on the ideal wife poem, with Psalm 112. Psalm 112:1-10 is an alphabetic acrostic about the ideal husband. The fear of YHWH, like at the end of Qoheleth (Ecclesiastes 12:13) is the preeminent trait of both the wife (Prov 31:30) and husband (Psalm 112:1). The point of Ecclesiastes is to explain the limits of wisdom and this seems to be a favorite feature of this conversation. Job makes a similar point. The limit on wisdom is that we should fear God and keep His Torah.
Thus the Writings make the point about Writings, “My son, beware of anything beyond these. Of making many books there is no end, and much study is a weariness of the flesh” (Ecclesiastes 12:12). We must keep this in conversation with how the delight of the blessed is in the written Torah of YHWH and on this Torah he meditates day and night (Psalm 1:2). Thus we should study (even toil until we are weary) the word of God. But this ending to the central book of the chiasm of the Writings is fitting. It is similar to ending the New Testament with the Book of Revelation given how Revelation ends warning about adding or subtracting from it. The effect of Ecclesiastes 12:12 is to say, the Writings are now complete until prophecy resumes, beware of adding to or subtracting from them.