The activity of God, which is transcendent in blessedness, is the activity of contemplation; and therefore among human activities that which is most akin to the divine activity of contemplation will be the greatest source of happiness.
For contemplation is both the highest form of activity (since the intellect is the highest thing in us, and the objects that it apprehends are the highest things that can be known), and also it is the most continuous, because we are more capable of continuous contemplation than we are of any practical activity.