The Constitution is an instrument of government. It is not a legal code nor an embidiment of eternal principles but a means of establishing and empowering a limited government. The Bill of Rights aimed to reduce its powers without crippling it. One that worked but did not subject the people to its rule as a kingdom might.
I believer you’re partially correct.
Yes, it is an instrument to setup a limited government. But it is as much legal code (IE: sets out what gov’t CAN do) as well as being an embodiment of principles, only ‘eternal’ in that gov’t must use the Amendment process to change.
To look at it any other way allows the distortion of limited gov’t and reduction of Freedom and Liberty by nefarious means.