I know about Messianic Jews. I generally consider them Christians, because that's exactly what they are if they believe in Jesus as the Messiah. I was talking about non-Christian Jews who are still waiting for their Messiah.
Most Christians are Gentiles. Messianic Jews are Jews in every way, except for their acceptance of Jesus as the Christ.
2 Thessalonians is a pseudepigraphal work, meaning it's a forgery. It wasn't written by Paul and should not be considered Scripture.
I don't believe that. I'll have to see some convincing evidence before I will.
Also, you claim that churches are no longer standing by the Bible. Are you referring to a literal Biblical interpretation? Because that doesn't stand up to scientific scrutiny. Christianity has never wholly stood by the Bible in a literal sense anyway; Biblical literalism is a recent phenomenon - a knee jerk reaction to the discovery of evolution.
Biblical literalism is not a new phenomenon. The Jews of Jesus time were split in two groups. The Pharisees were the literalists, and the Sadducees believed that angels, demons, and the afterlife were not real.
However, that is not what I was referring to. Churches are interpreting the Bible by their ideas, instead of forming their ideas around the Bible. For example, some Lutheran organizations have become gay-friendly. They no longer teach what the Bible says about homosexuality.
Also, seeing as Christians have been divided over doctrine since it started as a religion, it will be interesting to see which Church denomination wins the debate regarding what "standing by the Bible" actually means. For example, should Christians speak in tongues or not? Baptise infants or not? Preach "once saved always saved" or not? Practice the Baptism of the Holy Spirit or not? "Standing by the Bible" is much easier said than done.
Even in Paul's time, this was happening. The biggest reason for the many splits is the fact that most churches don't teach the Bible by what it actually says. They teach what they want to teach, cherrypicking from the Bible and misinterpreting however is convenient for them.
Speaking in tongues? Paul was very clear on that subject. It's not to be used too frequently, and not at all if there is no one to translate. Also, it is called the least of the gifts, not the greatest, as some churches teach.
The once-saved-always-saved debate is largely a matter of semantics. I've found that what people argue sounds very much the same. However, again, this is another topic that is not open for debate. The Bible teaches that:
1. God chooses salvation for us. It's not our choice.
2. If you fall from the faith, you cannot be saved a second time. Probably because were either never saved in the first place (a wolf in sheep's clothing). Because of 1., however, someone who returns to the faith could be said to have never lost their salvation.
3. Those who are saved will live accordingly. You can't simply say a prayer of faith once and expect to go to Heaven.
I'm not sure what you mean by baptism of the Holy Spirit. My experience with different denominations concerns sprinkling versus submersion, or "in the name of Jesus" versus "in the name of the Father, and of the Son, and of the Holy Spirit."
For the first, there is still no room for debate. The word "baptism" does not exist in Greek. It's a made up word made to sound like the Greek "baptiso," which means "immerse" or "bury." Baptism was a symbol of death to sin and resurrection to new life, and a believers baptism was also a symbol of Christ's burial and resurrection. Sprinkling was invented later, when Catholics figured it was easier that immersion, but sprinkling lacks the meaning of real baptism.
The second is based on the false belief some hold that Trinitarians believe in three gods. The command to baptize in the name of the Father, Son, and Holy Spirit comes from the last chapter of Matthew. Baptism in the name of Jesus is in the Bible too, so either way is valid.