Christ's promise to St. Peter was a guarantee of the truth. Now this is important because the devil being "a murderer and the father of lies" (Jn. 8:44) keeps on campaigning to bring as many as he could to eternal fire and perdition in Hell. That promise written in Mt. 16:18 runs like this: "You are Peter and on this rock I will build my Church. And the gates of the underworld can never hold out against it. I will give you the keys of the kingdom of heaven: Whatever you bind on earth shall be considered bound in heaven; whatever you loose on earth shall be considered loosed in heaven" (Mt. 16:18-19).
The original name of Peter was Simon, then was changed by Jesus to Peter, which means "rock" since as the first Pope he was to lead the Church. Till the present there have been already more than 250 popes. You can even read in the Guinness book of records, year 2001 that the Roman Catholic Church is the biggest religious denomination united under one head, the Pope, presently Pope Benedict XVI. It has continued throughout the centuries, inspite of enemies from within and without. The amazing thing is that none of its members are Catholics by force but are members of the Catholic fold in their free search and quest for truth. You can check for yourself, down through history and amid so many trials and difficulties, how the Lord has supported His Church by so many attestations of miraculous events and cures that serve to prove the truth of its existence as God's Church. This fact is narrated in the Bible when the Lord shows His approval by accompanying His closest servvants with extraordinary signs from heaven. "These signs will accompany those who believe: in my name they will drive out demons, they will speak new languages. They will pick up serpents (with their hands), and if they drink any deadly thing, it will not harm them. They will lay hands on the sick, and they will recover. So then the Lord Jesus, after he spoke to them, was taken up into heaven and took his seat at the right hand of God. But they went forth and preached everywhere, while the Lord worked with them and confirmed the word through accompanying signs' (Mk. 16:17-20).
Our main purpose in the search for the guarantee of truth is for the sake of reaching our final and true goal: heaven. Our enemy, the devil, and his agents (humans and co-devils) continue their campaign of lies with the purpose of bringing as many to the eternal fires and punishment of hell. Since our main objective is always to reach our goal of happiness with God, let's do what we can to avoid the deceptive lies of the devil and help one another, by God's grace and mercy to reach our true goal: heaven with the Triune God, Father, Son and the Holy Spirit, together with our Blessed Mother the Virgin Mary and all the angels and saints. Those to be admitted to the kingdom of heaven according to the book of Revelation 21:29 "Nothing unclean may come into it: no one who does what is loathsome or false, but only those who are listed in the Lamb's book of life" (Rev. 21:29).