What is the overall message of this poem?

the fly by william blake little fly, thy summer's play my thoughtless hand has brushed away. am not i a fly like thee? or art not thou a man like me? for i dance and drink & sing, till some blind hand shall brush my wing. if thought is life and strength & breath and the want of thought is death; then am i a happy fly, if i live, or if i die.

a)you should not kill other creatures because they also experience pain.

b)every creature on earth is at the mercy of some higher being.

c)flies live happier lives than people because they are free.

d)flies are important because they teach us to be humble.