Christianity must Implode

[Lek]

Jesus did come to the Jews, but his mission was to save all people.  This mission was handed on the his disciples to carry out to the rest of the world.

1 John 2:2 (ESV)
2 He is the propitiation for our sins, and not for ours only but also for the sins of the whole world.

Jesus said He was the Good Shepherd, and He predicted that His flock would be greatly expanded: “I have other sheep that are not of this sheep pen. I must bring them also. They too will listen to my voice, and there shall be one flock and one shepherd” (John 10:16).

Romans 1:16English Standard Version (ESV)
16 For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.

As for the image of the gate in the new Jerusalem, all believers are part of the new Israel:

Romans 9:6-8English Standard Version (ESV)
6 But it is not as though the word of God has failed. For not all who are descended from Israel belong to Israel, 7 and not all are children of Abraham because they are his offspring, but “Through Isaac shall your offspring be named.” 8 This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as offspring.

So the John character must have been more powerful than the Jesus character because he changed Jesus' self-stated mission.  

Since you are a believer what tribe did you join so that you can pass through one of the twelve gates?

I'm a member of the body of Christ, which is Israel. You're trying to take verses from an apocalyptic book, that is written entirely in symbolic language, as if the language is literal. You are also not looking at the bible as a whole.

"4 When you read this, you can perceive my insight into the mystery of Christ, 5 which was not made known to the sons of men in other generations as it has now been revealed to his holy apostles and prophets by the Spirit. 6 This mystery is[a] that the Gentiles are fellow heirs, members of the same body, and partakers of the promise in Christ Jesus through the gospel." Ephesians 3