This quote from William Shakespeare's play Macbeth is spoken by Macbeth himself. It is a reflection of his confidence in his own invincibility. He believes that he is protected by some kind of supernatural power, and that no matter what danger he faces, he will be able to endure it. This is a reflection of his ambition and his belief that he is destined for success. It is likewise a tip of the power of fate and destiny, and how it can shape our lives. Macbeth's belief in his own charmed life is eventually his downfall, as his ambition and hubris lead him to make decisions that eventually result in his own destruction. This quote acts as a suggestion that no matter how powerful we may feel, we are all based on the whims of fate.
"Life is life - whether in a cat, or dog or man. There is no difference there between a cat or a man. The idea of difference is a human conception for man's own advantage"