Matt. 16:18
And I say also unto thee, That thou art Peter (petros - proper masculine noun; a rock or stone detached, large fragment), and upon this rock (petra - femine noun - a large rock, cliff, ledge, massive living rock) I will build my church; and the gates of hell shall not prevail against it.
I suggest you look at something other than a Martin Luther translation.
Also, why the stuff about Peter’s authority on Earth and in Heaven?
http://www.iamonetruth.com/peter___rock.htm
Besides, Jesus spoke Aramaic, NOT Greek.
In the native tongue of Jesus, there was NO difference in the word!
“Some argue that in this passage there is a minor difference between the Greek term for Peter (Petros) and the term for rock (petra), yet they ignore the obvious explanation: petra, a feminine noun, has simply been modifed to have a masculine ending, since one would not refer to a man (Peter) as feminine. The change in the gender is purely for stylistic reasons.
These critics also neglect the fact that Jesus spoke Aramaic, and, as John 1:42 tells us, in everyday life he actually referred to Peter as Kepha or Cephas (depending on how it is transliterated). It is that term which is then translated into Greek as petros. Thus, what Jesus actually said to Peter in Aramaic was: “You are Kepha and on this very kepha I will build my Church.”
The Church Fathers, those Christians closest to the apostles in time, culture, and theological background, clearly understood that Jesus promised to build the Church on Peter, as the following passages show.”
http://www.catholic.com/library/Origins_of_Peter_as_Pope.asp