Last September the Reformed Forum crew had a fascinating and enlightening podcast concerning John Flavel & Union with Christ. Well worth listening to. And while you are there perhaps you can support the RF guys with a small donation.
From the Reformed Forum website...
Westminster Theological Journal.
In the article, Edwards demonstrates several interesting 17th c.
formulations of the doctrine of union with Christ. In doing so, Edwards
brings his findings into present discussion on the subject.