"...and upon this rock I will build my church..."

Church leaders base papal authority largely upon the statement in MT 16:18, “…you are Peter, and upon this rock I will build my church…”   The original Greek text of Matthew’s gospel actually uses two forms of the word “rock”, one masculine (petros) and one feminine (petra).  Re-inserting just the Greek words used for “rock”, the statement would read something like, “…you are Petros and upon this petra I will build my church…”

In Greek, the masculine and feminine forms of this word vary somewhat in meaning.  “Petros” means a rock as in a stone whereas “petra” means a rock that is a massive foundational formation.  Some biblical scholars debate over the shift in gender and meaning, mostly to question papal authority.  These scholars suggest that this verse means that Peter is a small fragment of the foundational rock or perhaps that the verse doesn’t refer directly to Peter at all.

Church leaders refute such arguments by explaining that Jesus would have spoken Aramaic, not Greek.  The Aramaic word of "kephas" has no gender and is the same word for stone, rock or foundational slab.  So if we insert Aramaic for “rock”, it would be, “…you are Kephas, and upon this kephas I will build my church…” In Aramaic, the rock's magnitude is either irrelevant or inferred.  

Though the Aramaic word doesn't really distinguish magnitude, the author chose the Greek word referring to a massive foundational structure for the word's second appearance.  Church leaders explain that proper speech would not permit using a feminine noun as a man’s name in the first instance.  Thus, it would have been improper speech to say, “…you are Petra, and upon this petra I will build my church…”

Church leaders explain why the Greek author didn’t use the all feminine Petra/petra combination.  The mixed gender Petros/petra combination is one alternative and the one that was used.  However, why didn’t the author of Matthew write it as, “…you are Petros, and upon this petros I will build my church…”?  This would have preserved the general meaning and maintained consistent masculine gender usage, “….you are a male rock, and upon this male rock I will build my church…”

Instead the author chose to change genders, “…you are a male rock, and upon this female rock I will build my church…”  I just wonder if there is any significance to referring to Peter as a female rock upon which to build the church.  In my research, I’ve not found anyone who explores this question.  Since church leaders give tremendous attention to gender in other passages about apostles, I just wonder why it has not been explored here.  It would seem to me that if the preservation of an all-male leadership team were important to early church leaders, they would have preferred using the masculine petros/petros combination rather than what the gospel author chose, the mixed gender "petros/petra" combination.