Petros means a stone like lithos and it is a male gender.
Petra means a big Rock which is female gender.
They are totally different.
I think Jesus spoke to Peter in Hebrew at that time.
Jesus called Peter "Kefa" but the Rock which Jesus was talking about ( Petra in Greek) was either Selah(5554) or Tsur (6697). I believe Selah is more possible than Tsur.It is mentioned in Isaiah 16:1.
You can find this at Crosswalk.com, in the foot notes:
http://bible.crosswalk.com/OnlineStudyBible/bible.cgi?new=1&word=Isaiah+16§ion=0&version=kjv&language=en#F85
Therefore Rock should be considered totally different from small stones (on the seaside.) which was kefa.
The Rock which has been the basis of the Church was not any corruptable human being, but the Truth which is actually Jesus Christ.
Look at these:
1 Cor 3:11 For other foundation can no man lay than that is laid, which is Jesus Christ.
Peter also mentioned Petra once again:
1 Peter 2:8
8 And a stone of stumbling, and a
rock of offence, even to them which stumble at the word, being disobedient: whereunto also they were appointed.
Here you can notice Peter use Petra of Offence indicating Jesus.
The fact that Jesus was mentioning female gender word, while indicating male gender for Peter, it means He separated two concepts.
How come Jesus condemn quickly Peter by saying " Get thee behind, Satan!" if Peter is the real foundation of the church?
Many people are trapped there because:
2 Thessalonian 2: 10-
because they received not the love of the truth, that they might be saved. 11 And for this cause God shall send them strong delusion, that they should believe a lie: