It’s easy to say the Bible is written around the unifying theme of Jesus, but it might be a little difficult to see exactly where He is sometimes. Words are used such as “promise” and “covenant” (essentially a promise too). But sometimes even those key words are absent such as in Genesis 3:15 when God promises (without using that word) a descendant who will crush the head of the serpent. Abraham was “promised” (using the word “covenant” instead) that this descendant would be from a child born to Sarah, who would “bless the nations.” Later on Isaac was called the “son of the promise” by Paul in places such as Romans 9:9 and that thought is tied with the “seed of Eve” all through the Bible. David was included in the promise. God said he would have a son who would sit on his throne in a kingdom that would last forever. This promised son and blessing was part of the gospel (good news) preached to Israel at Sinai (Hebrews 4:2). The Law was part of the promise because it lays out behavior expected by God as He takes up residence according to the promise. He took up residence in Israel and expected certain actions, and as He takes up residence now in believers those expectations have not changed.
If the Bible really is “one faith” (chapter 4) delivered to “one body” (chapter 3) by “one God” and “one Lord” (chapter 2) as Paul says in Ephesians 4 then the next question is “Why aren’t we (the church) following it?” If the New Covenant is the Law written on a heart of flesh, then it seems some biblical practices are being ignored by those who are supposed to have this covenant as their operating document. If the Bible really is one continuous, unified message (and it is) with no breaks or stops and starts or new bodies created then the next step is to grab hold and put it into every area of life. Not just as a novelty or for some chuckles once in a while but hungering and thirsting for it as if His Word was a treasure hidden in a field or a pearl of great price. I know I’m mixing metaphors but you get my drift.
All the books of the Bible were written by people who understood the continuity of this promise from God and included continuous revelation from God as to how this promise would be realized. All the believers throughout the ages who accepted God’s Word looked forward to the delivery of the promise and its full implementation. The first century church lived all of it. When we throw out parts of the Word, whether we dismiss them as merely “civil” or “ceremonial” shadows or “fulfill” them and terminate them, we destroy the unity and continuity of His living oracles. The promise (or promises since there are other parts to the promise) cannot be seen, hoped for, or realized as well as it could. Like a guitar with a string missing, or a violin without a bow, if we remove any part of His Word the gospel and the promises of God are reduced to a limited discordant series of feel-good proverbs lacking the power to move us as they are intended.