[Note: I'm not sure how well you know churches in the US.
First of all, nobody needs to know that which is man made and NOT according to Scripture, if it differes from the pattern of the apostles.
1 Cor. 1:13 "Is Christ divided?...."
1 Cor. 1:10 "...speak the same thing, and that there be NO divisions among u...."
This is a forum for the United Church of Christ (UCC). The UCC is a "mainline" church. It believes slightly different things from many other people in Christian Forums.
1 Tim. 1:3 "...teach no other doctrine."
2 Tim. 1:13 "Hold fast the pattern of sound words which u have heard from me, in faith and love which r in Christ Jesus."
Titus 1:9 "holding fast the faithful word he has been taught, that he may be able, by sound doctrine, both to exhort and convict those who contradict."
1 Tim. 4:13 "Take heed to urself and to the doctrine. Continue in them, for in doing this u will save both urself and those who hear u."
Matt. 28:20 "teaching them to observe all things that I have commanded u...."
Eph. 4:4 "There is ONE body and ONE Spirit, just as u were called in ONE hope of ur calling;"
5 "ONE Lord, ONE FAITH, ONE baptism
Rev. 22 regarding adding to, or taking away from His word.
I'm a member of a different mainline church, the Presbyterian Church (USA). I'm going to give you a mainline answer to your question. (Of course one thing about the mainline is that we don't all agree with each other. So this is just one answer. But many postings here are by people who are not part of the UCC or any other mainline church.)]
1 Cor. 3:11 "For no other foundation can anyone lay than that which is laid, which is Jesus Christ."
Acts 5:29 "...we ought to obey God rather than men."
Gal. 1 It gives a warning 2 times about preaching any other gospel.
Jesus gives us an answer to this question. He says he has come to teach the "good news" (the Gospel). The good news says that he is bringing the Kingdom of God. In the Lord's prayer he teaches us to pray for God to bring his Kingdom to earth. Many of his parables are about the Kingdom.
What is the Kingdom of God?
A kingdom is where a king rules. So the Kingdom of God is where God is in charge. That is, it is where people follow God. The full Kingdom won't be here completely until the end of time. But it is here today among Jesus' followers. It is like the seed growing secretly in one of Jesus' stories.
How did Jesus establish the Kingdom?
* By teaching about God: God loves us. He wants us to turn away from our sins, so he can forgive us.
* By welcoming and forgiving everyone. He even welcomed people who were sinners. Many of them were people that the religious leaders looked down on.
Yes, but they did not retain their sins, if they were penitent.
* By healing people. This showed God's power and God's desire to help us.
* By dying for us.
How did his death help set up the Kingdom?
The night before Jesus died he shared a meal with his followers, the Last Supper. At that meal he blessed the bread and wine, saying "This is my blood of the new covenant." The new covenant is a reference to Jeremiah 31:31. In that passage the Prophet Jeremiah speaks about a new covenant. In that covenant God would change people's hearts. The Kingdom of God is the people who follow that covenant.
The new covenant is the N.T.
In the Old Testament, establishing a covenant required a sacrifice. There were sacrifices by Noah, Abraham, and Moses when their covenants were established. Jesus' death was the sacrifice for the new covenant. In the Old Testament, sacrifices were normally done by people who sinned. They showed the person's repentance, and dedication to change.
I believe Jesus' death was an act of repentance on our behalf. In Roman 6, Paul says that when we become Christians, in baptism, we die to sin with Christ, and rise with him to new life. He is saying that the Holy Spirit unites us to Christ, and then by being with Christ in death and resurrection, we leave our sins and get new lives.
Jesus was the ultimate sacrifice and is our High Priest forever.
Heb. 4:14 "...we have a great High Priest who has passed through the heavens, Jesus the Son of God...."
Where is the Kingdom now?
At the end of time, the Kingdom of God will be everywhere.
The kingdom of God is being preached and spreading = His church
At the moment it is present with Christ's followers. But we aren't supposed to keep it private. In the Great Commission, Jesus sends us into the world. Our mission is to bring everyone into the Kingdom, by telling them about Jesus, and by showing his love to them.
But the Kingdom of God isn't just individuals. It's the Church, a community of those who follow Jesus. We show the love of God by how we treat others in the Church. Members of the Church help each other bring the Kingdom to others.