Selection from – Ethics – Part V. On the Power of the Intellect; or of Human Freedom (Page 3)
Spinoza's Words: (knowledge of how to increase one's power brings joy)
He who would govern his emotions and appetite solely by the love of freedom strives, as far as he can, to gain a knowledge of the virtues and their causes, and to fill his spirit with the joy which arises from the true knowledge of them: he will in no wise desire to dwell on men's faults, or to carp at his fellows, or to revel in a false show of freedom.
Whosoever will diligently observe and practice these precepts (which indeed are not difficult) will verily, in a short space of time, be able, for the most part, to direct his actions according to the commandments of reason.
Comment:
In Part IV Spinoza defined virtue as a man's power of acting in the world. Here he recommends finding ways to do that and says that the knowledge gained will help one act rationally. Remember that power for Spinoza is increasing one's existence in the world without hurting anyone else.