"Ignorance is strength" means that if you believe everything what they say to you and ignore what is really behind, the state and the government will have all the power they want to do wathever they want. The government in that times thought that if the population doesn't know anthing and they can lie to them, everybody will believe in them and no weaknesses within what the government says will never be found, so it gave strength to the parties and the government. So, the ignorance of the population gave strength to the state.
That sentence helped me to understand better the thoughts of the state and the parties in that time and the problems of the society that are really different to our times.
