The twelve Apostles were not preaching the same gospel as Paul, but rather the gospel of the kingdom, which Paul never preached.
It is imperative to believe the gospel that was given to us and be justified unto eternal life.
Yes, at least to the second, certainly. I have a lot of catching up to do, having not grown up really with teachers who talked about dispensationalism or the big ideas in Pauline theology or the details of the end times (which I realize are important to understand, as much as the average person can...Revelation 22:7 "Behold, I am coming soon! Blessed is he who keeps the words of the prophecy in this book.") My mind is reeling a bit from having to change my opinions a lot in only a short time...
This is what I've gleaned from reading in this thread. The Kingdom is in heaven. It is in the hearts of those believers who are in the Body of Christ according to the mystery as preached by Paul. It was in the hearts of some who believed Jesus while he preached. A form of the kingdom will exist on the earth, to be ruled by Christ and certain of the Jews, in the future. I'm not sure which earth this necessarily is, but I am open to suggestion. Aside from these manifestations, the Kingdom will exist forever, for all Jews and Gentiles who are justified.
Paul says new things in his epistles. These are perfectly in line with what Christ taught (John 3:18 "Whoever believes in him is not condemned, but whoever does not believe stands condemned already because he has not believed in the name of God's one and only Son." (NIV) Paul explained further what is said here (that nobody at this time has to follow the bulk of the law's regulations) and further spelled out doctrines of faith, the elect, and Christian kindness.
Peter and Paul do not seem to have preached the exact message regarding every regulation (luckily I am virtually a vegetarian and don't normally have to worry about how meat has been slaughtered). So, at least in some sense, Paul's message IS different.
But are you saying that the message Jesus preached during the few years of His earthly ministry did still at that point include all the regulations of the law? If so, I am open to the teaching (unless I am forgetting a line of Scripture that clearly denies this, and if this can be reconciled with the quote from John above). However, that would seem not to be very relevant to us, especially if the end times have not truly begun yet? Please help me out if you think I'm going off the rails at any point...I am not sure about some things yet.
May God bless you in every way through His Son Our Lord Jesus Christ.