"IS" of Identity, or "IS" of Prediction in the Trinity

At 30 minutes and 33 seconds of the following video, William Lane Craig distinguishes between the "is" of identity and the "is" of prediction with respect to the doctrine of the Trinity.

Cued Up Direct Link Below 
https://youtu.be/dqgju6FOzIo?t=30m33s

See also my blogpost:

William Lane Craig's Introductory Lectures on the Trinity