Peter Martyr Vermigli was an Italian Reformer who ended up being very significant in the English Reformation.  His Loci Communes (Common Places) were published after his death.  They consist in portions of his commentaries and other writings which are organized according to the pattern of what we would today call "Systematic Theology."  This is a very important work for understanding early Reformed theology.  In one of the chapters, he deals with the difference between the old and new covenants (or "leagues" as it is translated).