The church of Christ, which is the kingdom of Christ, is the greatest institution in all the world! It was built by Jesus Christ Himself (Matthew 16:18). It was purchased with His blood (Acts 20:28). The church is made up of all the saved (Ephesians 5:23). It will be given back to God, the Father, at the second coming of Christ (1 Corinthians 15:24-26). Therefore, only those who are in His church (kingdom) will be saved.
Note that the church of Christ was planned by God from eternity! But sometimes, false teachers tell us and kept emphasizing on it that Jesus came to establish a kingdom on this earth, as if it was the real deal.
Some even worsened it as they further say “He failed because the Jews rejected Him. Therefore, He set up the church as a substitute. He will come the next time to set up His kingdom“. Their claim is not true! Be aware, as the Holy Spirit bear witness, that Christ came at the right time (Galatians 4:4,5). He set up the church (kingdom) as God had planned before the earth was created. Glory be to GOD!
“To the intent that now the manifold wisdom of God might be made known by the church to the principalities and powers in the heavenly places, according to the eternal purpose which He accomplished in Christ Jesus our Lord” (Ephesians 3:10,11).