"Tis a fault to Heaven, A fault against the dead, a fault to nature, To reason most absurd" What does it mean?

Answer 1

This quote means: that to reason you cause fault in Heaven, against the dead and nature. In other words, don't question things.

Answer 2

Quick guess-
Life and the Universe and whatever is set up in one specific way, according to one set of principles.
To reason most absurd, to contradict the norm, is sacreligious, or nearly so.
Of course, that's bunk, because that means-
Don't be unique, and don't think for yourself.
I'd rather be crazy and independent.
Oh, well, I am. That explains it, of course.

Answer 3

replace the word "fault" and "absurd" with "wrong" then you have the essence of the meaning.