The synopsis of Book III is short and deals with the Trinity and the divine persons. However, don’t let the length of the synopsis fool you. The actual discussion in the main text is 38 pages. Those pages are packed full of theological meat and potatoes.
The persons of the Deity are three in number: the Father, the Son, and the Holy Spirit.
The divine persons are everywhere considered either communally or singularly.
Singularly, they are considered either absolutely or relatively.
Relatively, insofar as they have respect either to essence or to the other persons.
The persons compared to the other persons are considered both in regards to communion and in regards to their distinctives.
The persons are distinguished accorded to source (originem), order and their operations.
The distinction of the persons according to their operations is two-fold: either with regards to the mode of operation in essence, or with regards to personal operation.
Thus far with regards to the essence of God. What follows concerns his works.