God had promised that He would restore Israel and the Prophet Joel had prophesied how they would know when this restoration would begin. So when Peter preaches on the day of Pentecost, He begins with this statement: "But this is that which was spoken by the prophet Joel" (Acts 2:16). Peter is preaching a message of restoration for the nation Israel. Not Jew and Gentile.
But why was Peter convinced that this was indeed Joel's prophecy coming to pass?
"And it shall come to pass afterward, that I will pour out my spirit upon all flesh; and your sons and your daughters shall prophesy, your old men shall dream dreams, your young men shall see visions: And also upon the servants and upon the handmaids in THOSE DAYS will I pour out my spirit.
And I will shew wonders in the heavens and in the earth, blood, and fire, and pillars of smoke. The sun shall be turned into darkness, and the moon into blood, before THE GREAT AND THE TERRIBLE DAY OF THE LORD COME.
And it shall come to pass, that whosoever shall call on the name of the Lord shall be delivered: for IN MOUNT ZION and IN JERUSALEM shall be deliverance, as the Lord hath said, and in the remnant whom the Lord shall call." Joel 2:28-32.
When the day of Pentecost had fully come, there came a sound from heaven as of a mightly rushing wind, there appeared unto them cloven tongues like as of fire, and it sat on each of them. And they were ALL filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. Acts2:1-4.
When God's spirit was poured out on them on the day of Pentecost, they knew what that meant. That Joel's prophecy was coming true. The next part of his prophecy was about the great and terrible day of the Lord (tribulation), then the return of Christ the Messian to set up His Kingdom. They were waiting for those next prophecies to begin. And they were convinced that Christ was about to return to set up His Kingdom.
The reason that 12th disciple had to be chosen before the day of Pentecost was because Christ had promised them in Matthew 19:28: "And Jesus said unto them, Verily I say unto you. That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel." Luke 22:30 also speaks of this. There HAD to be 12 Disciples to sit upon the 12 Thrones judging the 12 tribes of Israel. Before Christ 2nd coming, that throne position judging Israel HAD to be filled. He would not have come back to an empty throne for the 12 tribes of Israel.
First of all, you ask one of my favorite questions. Why?
I understand what you are saying about Peter and what the others believed regarding how soon Christ was going to return.
It’s is what I have believed also, and as you say, the sermon in Acts supports that.
I do not claim that Peter immediately knew everything or that he did not develop in His understanding of the message as time went on. I think we can agree that would be wrong.
It is very possible that Paul came along with his revelations and clarified or opened the others eyes to the message of grace.
But, I do not believe that the he was given a different gospel. Remember, Jesus promised that the Holy Spirit would come and lead them to all truth and remind them of what He had taught them.
Paul may have been how the Holy Spirit came to the others to lead them where Jesus wanted them to go in forming the message. We know that many Jews did not accept the message and the Bible prophecies that as well as the fact that the message would be delivered to the Gentiles because of their rejection.
But, a different Gospel? I don’t agree with that. A refining of the message? That I could see.
Catholics are always amazed when converts come into the Church. They bring fresh eyes and a zeal and love for Jesus and the Church.
It is not that cradle Catholics do not love Jesus or the Church. It is more a taking things for granted kind of attitude. And so new Catholics can remind us of the wonders and riches of our faith.