The highest good is the knowledge of God
Formal Statement
The mind's highest good is the knowledge of God, and the mind's highest virtue is to know God.
In Plain Language
This sounds religious, but recall what "God" means here: the whole of Nature understood through its necessary laws. The "knowledge of God" is not piety — it is the deepest possible adequate understanding of reality. And since adequate understanding generates joy (it is an increase in the mind's power), the knowledge of God is simultaneously the highest intellectual achievement and the most stable source of positive affect. Freedom is cognitive before it is moralistic: you do not first discipline your will and then learn about God; you learn about reality, and the discipline follows.
Why This Follows
Step 8 (df-08) showed the mind can know God's essence. Step 13 (df-13) showed that freedom requires affects strong enough to overcome passive emotions. This step identifies the affect that is strongest of all: the joy of understanding God/Nature, which is adequate, self-sustaining, and not dependent on external fortune.
Freedom is fundamentally cognitive — understanding God/Nature is the highest good.
Connected Concepts
If "knowledge of God" just means deep understanding of natural necessity, why does Spinoza keep using the word "God" at all? What work does the word do?