William Blake (1757-1827) was a poet and philosopher who had a huge impact on the Romantic movement. The Romantic movement was a reaction to the increased rationalist, scientific viewpoint that was coming into vogue. It valued strong emotion above all else, in all forms - not only love, but also horror, terror, and awe.
Basically, if you value freedom of expression, your thoughts probably owe a heavy debt to the Romantic philosophers and artists from the end of the 18th century to the middle of the 19th century.
Proverbs of Hell 9, from William Blake's Marriage of Heaven and Hell
The fox provides for himself, but God provides for the lion.
Think in the morning. Act in the noon. Eat in the evening. Sleep in the night.
He who has suffer'd you to impose on him knows you.
As the plow follows words, so God rewards prayers.
The tygers of wrath are wiser than the horses of instruction.
Expect poison from the standing water.
You never know what is enough unless you know what is more than enough.
Listen to the fools reproach! it is a kingly title!
The eyes of fire, the nostrils of air, the mouth of water, the beard of earth.
The weak in courage is strong in cunning.
The apple tree never asks the beech how he shall grow, nor the lion, the horse, how he shall take his prey.
The thankful reciever bears a plentiful harvest.
If others had not been foolish, we should be so.
The soul of sweet delight, can never be defil'd.
When thou seest an Eagle, thou seest a portion of Genius, lift up thy head!
As the catterpiller chooses the fairest leaves to lay her eggs on, so the priest lays his curse on the fairest joys.
To create a little flower is the labour of ages.
Damn, braces: Bless relaxes.
The best wine is the oldest, the best water the newest.
Prayers plow not! Praises reap not!
Joys laugh not! Sorrows weep not!
Blake was a poet, but even moreso a philosopher. He's probably one of the least read and most important poets of his time, and part of this is because of how incredibly dense his work is.
Just to give you one example, in his work (partly based on imagery familiar to most people of his time) horses represent reason and tigers represent wrath and its logical conclusion, revolution. So the line The tygers of wrath are wiser than the horses of instruction is stating that the deep impulses of our minds, such as wrath, are more wise than rote rationalization that we have trained into our minds.
In essence, this poem (and its larger whole) are arguing that people need to express our less rational and more emotional aspects in order to escape the repressive nature of conventional morality and religion. Blake believed that reason and emotion were at war in every person, and that people who tended toward either side were both necessary to keep the world in balance.
Which are you? An "energetic creator" or a "rational organizer"?
Personally, I am tired after thinking about Blake this much!