Hi Selene,
It doesn't matter what language Jesus Christ spoke, because the NT was written by Greek-speakers who knew its vocabulary and construction. It is inconceivable that they would choose the wrong word for 'rock' or 'stone', just like you would not confuse the two when speaking in English.
More importantly, this passage was written by an eye witness that experienced the moment. When Matthew wrote this, he knew what he intended to convey.
Mat 16:18 And I say also unto thee, That thou art Peter (petros), and upon this rock(petra) I will build my church; and the gates of hell shall not prevail against it.
Matthew used two different words here that the translators rendered "rock". Now, who was the head of the church?
Act 15:13 And after they had held their peace,
James answered, saying, Men and brethren, hearken unto me:
Act 15:19 Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God:
James!
From Bullinger's notes...
Matthew 16:18
I say also = I also say (as well as the Father), looking back to a preceding Agent with Whom the Lord associates Himself.
thou art Peter. See App-147.
Peter. Greek. petros. A stone (loose and movable), as in Joh_1:42.
this. Very emphatic, as though pointing to Himself. See notes on Joh_2:19; Joh_6:58. One of three important passages where "this" stands for the speaker. See notes on Joh_2:19, and Joh_6:58.
this rock = Greek. petra. Petra is Feminine, and therefore could not refer to Peter; but, if it refers to Peter's confession, then it would agree with homologia (which is feminine), and is rendered confession in 1Ti_6:13, and profession in 1Ti_6:12. Heb_3:1; Heb_4:14; Heb_10:23. Compare 2Co_9:13. Whether we are to understand it (with Augustine and Jerome) as implying "thou hast said [it]" (see App-147), or "thou art Peter", most Protestants as well as these ancient "Fathers" agree that Peter's confession is the foundation to which Christ referred, and not Peter himself. He was neither the foundation nor the builder (a poor builder, Mat_16:23) but Christ alone, Whom he had confessed (1Co_3:11). Thus ends the great subject of this second portion of the Lord's ministry. See App-119.
rock. Greek. petra. A rock (in situ) immovable: the Messiah, as being "the Son of the living God", Who is the foretold "foundation-stone" (Isa_28:16); and the rejected stone (Psa_118:22).
will = shall. Therefore then future, as in Hos_1:10; Hos_2:23.
church = assembly. Defined as "Israel", and the "Remnant" (Rom_9:2, Rom_9:1-27). Not the ecclesia of the mystery (or secret) revealed in Ephesians; but that referred to in Psa_22:22, Psa_22:25, &c.
the gates. Put by Figure of speech Metonymy (of Adjunct), App-6, for power.
the gates of hell = the gates of Hades (= THE grave), denoting the power of the grave to retain, as in Isa_38:10. Job_38:17 (Septuagint) Psa_9:13; Psa_107:18.
hell = THE grave. Greek. Hades. See App-131.
prevail. Greek. katischuo. Occurs only here and Luk_23:23 = have full strength, to another's detriment: i.e. THE grave shall not have power to retain its captives, because Christ holdeth the keys of those gates, and they shall not be strong enough to triumph (Rev_1:18. Compare Psa_68:20). Resurrection is the great truth asserted here. Compare Eze_37:11-14. Act_2:29-31. 1Co_15:55. Hos_13:14.
So, Peter was a moveable stone and Christ was the Rock...
Mat 21:42 Jesus saith unto them, Did ye never read in the scriptures, The stone which the builders rejected, the same is become the head of the corner: this is the Lord's doing, and it is marvellous in our eyes?
Eph 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
There was a Simon that went to Rome, but it was not Simon Peter...