The prominence of diatheke in the Epistle to the Hebrews made its interpretation crucial to the development of federal theology, and therefore Hebrews provides the natural starting point for an exegetical history of this topic. Since either producing merely a specimen of Hebrews exegesis or surverying broadly the exegesis in our period will raise more questions than it will answer, this project has been conceived in two parts. The first demonstrates the crucial role Hebrews exegesis played in the sixteenth and seventeenth centuries, providing necessary context. The second part explores in detail the Hebrews exegesis of a particular federal theologian, Johannes Cocceius (1603-1669), who is generally regarded as a high-water mark in the development of this doctrine. These two parts together demonstrate that exegesis was crucial in the development of federal theology, and therefore is a necessary and oft-neglected avenue to understanding this doctrine and its development. - Statement of the thesis.