What is the origin of the Covenant of Grace?

In Covenant Theology the [**Covenant of Grace**](http://en.wikipedia.org/wiki/Covenant_theology#Covenant_of_grace) refers to an overarching theological covenant which God made on the basis of grace. The various Biblical covenants such as Abraham's, the Mosaic/Deuteronomic, and David's are considered to be expressions, administrations, or even (ironically) dispensations of the single original Covenant of Grace. The Covenant of Grace is timeless, an eternal agreement that God will graciously save his people, on the basis of which God made other specific covenants like Abraham's etc. 1. Who first developed this concept of the Covenant of Grace? 2. Were the other two metacovenants of Covenant Theology, the Covenants of Redemption and Works, developed at the same time? 3. Are there any substantial differences from how the Covenant of Grace was first conceptualised compared to how it is understood now?