Mah inyan shemitta etzel torat kohanim likens the specificity of the laws of shemitta with the specificity of the laws of the mishkan.
The laws of shemitta differ from the laws of the mishkan in that the laws of shemitta do not have an analogue to what parshiot Terumah, Tetzaveh, Vayaqhel and Piqudei represent for the laws of the mishkan. The Chumash does not spell out the positive institution-building activities those who keep the laws of shemitta need to undertake during the six active years.
Why is there no shemitta analogue in the Bible to the exacting details presented for the building and erecting of the mishkan? We have a hint in Leviticus 26 when God says that if Israel walks in the chuqot and does the mitzvot of shemitta He will reside among them in a sort of pre-mishkan fashion.
That reference invokes the notion of goel es nephesh even though the entire frame did not mention the mishpatim of shemitta. One would surmise therefrom that the mishpatim of shemitta refer to the institutional sub-structure of keeping the laws of shemitta. To build that sub-structure is tantamount to having God in the Children of Israel’s midst in a fashion that is pre-egel masseikha.