Here is a short extract from Hodge on the various ways the New Testament speaks of the Mosaic covenant:
(1.) When viewed in relation to the people of God before the advent, it is represented as divine and obligatory.
(2.) When viewed in relation to the state of the Church after the advent, it is declared to be obsolete. It is represented as the lifeless husk from which the living kernel and germ have been extracted …
(3.) When viewed according to its true import and design as a preparatory dispensation of the covenant of grace, it is spoken of as preaching the same gospel, the same method of salvation as that which the apostles preached.
(4.) When viewed, in the light in which it was regarded by those who rejected the gospel, as a mere legal system, it was declared to be a ministration of death and condemnation. (2 Cor. iii. 6-18.)
(5.) And when contrasted with the new or Christian economy, as a different mode of revealing the same covenant, it is spoken of as a state of tutelage and bondage, far different from the freedom and filial spirit of the dispensation under which we now live.”
Systematic Theology, 2:376
I think this is a very helpful summary to keep in mind when trying to understand how the NT speaks of the Mosaic Economy, which, as any observer of the current reformed scene knows, is a matter of some controversy!