ΚΑΤΑ ΜΑΤΘΑΙΟΝ 16:18
18 καγω δε σοι λεγω οτι συ ει πετρος και επι ταυτη τη πετρα οικοδομησω μου την εκκλησιαν και πυλαι αδου ου κατισχυσουσιν αυτης
Here both Petros and Petra is used. Some say that petra had to be changed into petros because St Peter is a man and therefore we need the masculine form. Do nouns in Greek have different genders? If petros is the word used once why not just change the second petra to petros? Is there something grammatical why they needed to keep the feminine petra (or is it theology)?
thank you for your inquiry. As far as I know, this was not the apostle's real name, but a nickname that Jesus gave him. Now, there's a coincidental wordplay that occurs, since the old Greek word for "stone" is attested as both "petros" and "petra", the first being masculine and the second feminine in grammatical gender. "Petros" is a literal translation of the Syriac word "kefa" (see etymonline.com, lemma: Peter), which is feminine. It would be difficult to attribute a feminine name to a male person in Greek, so it was somehow convenient that there was a masculine morphology, too. It wasn't changed - since the word existed already - but it was a matter of preference in terms of accuracy and propriety of the translator. Otherwise, something else would have undoubtedly been invented.
Some Greek nouns are attested with two genders, indeed. Usually, there is no significant variety in meaning, but this little "word-game" that occurs in the above sentence is that Jesus names Simon as "Petros" and then - probably - identifies him with a stone, i.e. something really stable, in order to found his church. So, I believe that Simon is actually given a symbolic name of this stability (well, I am not a theologian to precisely interpret this), but the genders' flexibility in the translation must have played their role in linking Jesus' intentions. For, as I mentioned before, it would have been unusual in Greek to attribute a female name to a male person. Whereas the Syriac word "kefa" probably implies that, a gender's function is independent of such conventions and restrictions. After all, a matter of culture and mentality, I would say.
Hope this helped a bit. Have a nice Sunday and let me know, whether I could be of further assistance.