The Old Testament begins with Genesis, and even though it is attributed to Moses it could have stood alone before Moses came about as it can be seen to be a Bible in itself that covered a wide variety of theological topics. What is interesting about Genesis is that it begins with the Garden of Eden in Genesis 2 with the fall, and Revelation 22 ends the last book of the Bible with a return to the Garden of Eden. The return is marked in Revelation 22:2 with the tree of life, and this is the same tree that is mentioned in Genesis 3:22 at the very beginning of the Bible. The point is that both Genesis and Revelation had been written thousands of years apart, but one is the clear introduction and the other is the clear conclusion because Revelation fulfills Genesis (as can be seen with the tree of life).
When Moses came he established Exodus, Leviticus, Numbers, and Deuteronomy as each book acts as a testimony to the covenant of God with the nation of Israel, and each book contains teachings concerning what to do and what not to do. The New Testament begins with the same type of quadruple set as it contains Matthew, Mark, Luke, and John as all four give new teachings about what to do and what not to do, but what is unique about the four gospels is that they give instruction on faith. The four gospels are intended to elaborate upon faith the same way that Exodus, Leviticus, Numbers, and Deuteronomy elaborated upon law. Both the four gospels and the four books of the law act as introductions to root the rest of the covenant by.
The book or Joshua shows the advance of the nation of Israel into the Promised Land just like the book of Acts shows the advance of the Church into various parts of the world. The book of Acts shows a conquest of a spiritual kingdom over the entire known world, but the book of Joshua shows Israel conquering many nations and gaining the Promised Land. Overall, one could even note that after Joshua is Judges and after Acts is Romans, and both Judges and Romans reflect the operation of God’s government on earth by going into detail concerning its wisdom and how it is ruled.
One could thus see that both the Old Testament and the New Testament are formulated to mirror one another. The order of the books and the content of the books was no accident, and both testaments have much the same order to them. The big difference between the two testaments is that the Old Testament teaches a worldly kingdom ruled by God whereas the New Testament teaches a spiritual kingdom ruled by God.