"He saith unto them, But whom say ye that I am? And Simon Peter answered and said, "Thou art the Christ, the Son of the living God."" And Jesus answered and said unto him, Blessed art thou, Simon Bar–jona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it. And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven. Then charged he his disciples that they should tell no man that he was Jesus the Christ."
(Matthew 16:15-20)

The question which Jesus Christ asks, is fulfilled by Simon-Peter's answer:

Thou art the Christ, the Son of the living God.

This is the revelation of the Gospel of Salvation as we will see throughout scripture where one believes... comes to the knowledge of Jesus Christ as the Son of God. This is the very element of acknowledgement of exactly WHO He is and what He did for us, since no one else fits that description. In other words, there is no confusion about WHO is being spoken of, or believed in.

"Whosoever believeth that Jesus is the Christ is born of God: and every one that loveth him that begat loveth him also that is begotten of him."
(1 John 5:1)

"But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name."
(John 20:31)

We are given a guarantee of salvation through this belief, which confirms who those people are, that are part of the Body of Christ... THE Church of Christ.
This ROCK spoken of, is the unbreakeable certainty of salvation through THE Gospel of Salvation, being sealed by the Holy Spirit, Jesus Christ the Cornerstone.

"And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ."
(1 Corinthians 10:4)

"In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,"
(Ephesians 1:13)

"If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel , which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister; Who now rejoice in my sufferings for you, and fill up that which is behind of the afflictions of Christ in my flesh for his body’s sake, which is the church: Whereof I am made a minister, according to the dispensation of God which is given to me for you, to fulfil the word of God; Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints: To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory: Whom we preach, warning every man, and teaching every man in all wisdom; that we may present every man perfect in Christ Jesus:"
(Colossians 1:23-28)

To summerize thus far, we are saved when we believe in Jesus Christ, the one who died for our sins, was buried and rose again. It is upon this Gospel I've just presented, that we stand, THE ROCK our foundation, bringing us into the Body of Christ, which is His Church. We are now perfect in Christ Jesus, being made saints and presented absolutely perfect.

This portion of the revelation, is described clearly in (Mark 16:17-18)
"And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues; They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover."

The gates of Hell is representative of strongholds of evil, that which secures an estate of sorts. Believers are attacked all the time, and if one is complacent in their belief, they may give way to strongholds which establish roots and foundations in our life, securing us from becoming warriors for Christ.

If we put on the full armour of God, and take action by the word of God, we can learn how to break those contracts/agreements, and cast the enemy out, destroying those gateways that let them in.

At the end of the day, The Gospel demonstrates what saves, and right after that, we're shown what life we're supposed to be living. We have an unbreakable faith, with the authority to affect war in spiritual places, destrying the strongholds of the enemy, having the power of binding and loosing through Jesus Christ. (See It is Time.)

If a belief system cannot adhere to the basics of the Gospel of salvation, and teach an accursed gospel, you can expect to find corrupted interpretations.
A prime example of this can be found in Catholicism where they completely miss the revelation in Matthew 16:15-20, mutilating the English language to make Simon-Peter the rock (See 'Is Peter the rock?') in an attempt to establish some papal lineage. This also creates masses of contradictions with the rest of scripture by placing the Gospel of Salvation upon Peter as Christ. This can only be described as actual heresey.

Taking this a step further, Catholicism then misreads "the gates of hell shall not prevail against it", as if any opposition to Catholicism is Hell coming against it.

This interpretation fails to recognize the basics of spiritual warfare true believers take against the forces of darkness in setting the captives free !!