The number 66’s significance with regard to the scripture can be found in its two main factors of 6 and 11. Both of these numbers are used in the scriptures to point to the great divide between man and God. 6 is the number of man in the scriptures and it is used in contrast to the number of God, 3. 11 is used in the scriptures in two main ways. The first is the faithfulness of God and the second is man falling short (see the number 11).
There are 66 books in the Bible because the entire Bible from beginning to end is about the faithfulness of God and man’s need for the Savior.
The book of Isaiah has 66 chapters and is a summary book for the entire Bible. The book of Isaiah is quoted 66 times in the New Testament. The division between the Old Testament and New Testament is seen in the book of Isaiah where there is a noticeable change in style between the 39th and 40th chapter. Malachi is the 39th book of the Bible and last book of the Old Testament. The prophecy of John the Baptist as the one who would prepare the way of the Lord is given in Isaiah 40 and is fulfilled in Matthew, the 40th book of the Bible.
Matthew 4:4 says,
4 But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God.
Leviticus 24:6 speaking of the showbread in the temple of the Lord says,
6 And thou shalt set them in two rows, six on a row, upon the pure table before the Lord.
So there were twelve cakes of fine flour to point to the twelve tribes of Israel but they were arranged in two rows of 6 to point to the completed revelation of God; 66 books of spiritual bread which man can and shall live by.
One final reference to the number 66 in the scriptures.
1 Kings 8:66 says,
66 On the eighth day he sent the people away: and they blessed the king, and went unto their tents joyful and glad of heart for all the goodness that the Lord had done for David his servant, and for Israel his people.
Read this scripture in a prophetic context. The seventh day of world history is the millennium. The eighth day is the new heavens and the new earth. The Lord Jesus Christ is the blessed king. Please note the chapter and verse. The new heavens and the new earth are mentioned in Isaiah 66:22 (also 65:17) and they are also mentioned in the 66th book of the Bible, Revelation in its last two chapters, 21 and 22.
The number 66 is pointing us to a day of joy and gladness of heart for all the goodness the Lord has done.