What is the difference between the Old Testament and the New Testament?

Ephesians 2:11-17 Therefore remember that you, once Gentiles in the flesh–who are called Uncircumcision by what is called the Circumcision made in the flesh by hands– (12) that at that time you were without Christ, being aliens from the commonwealth of Israel and strangers from the covenants of promise, having no hope and without God in the world. (13) But now in Christ Jesus you who once were far off have been brought near by the blood of Christ. (14) For He Himself is our peace, who has made both one, and has broken down the middle wall of separation, (15) having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace, (16) and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity. (17) And He came and preached peace to you who were afar off and to those who were near.
Hebrews 10:1-4 For the law, having a shadow of the good things to come, and not the very image of the things, can never with these same sacrifices, which they offer continually year by year, make those who approach perfect. (2) For then would they not have ceased to be offered? For the worshipers, once purified, would have had no more consciousness of sins. (3) But in those sacrifices there is a reminder of sins every year. (4) For it is not possible that the blood of bulls and goats could take away sins.

Who has the right to say what the church is and who the members are?

John 10:14 I am the good shepherd; and I know My sheep, and am known by My own.
John 10:27 My sheep hear My voice, and I know them, and they follow Me.

How can we believe there is one true church without being judgmental?

Ephesians 4:4-6 There is one body and one Spirit, just as you were called in one hope of your calling; (5) one Lord, one faith, one baptism; (6) one God and Father of all, who is above all, and through all, and in you all.
2 John 1:9-11 Whoever transgresses and does not abide in the doctrine of Christ does not have God. He who abides in the doctrine of Christ has both the Father and the Son. (10) If anyone comes to you and does not bring this doctrine, do not receive him into your house nor greet him; (11) for he who greets him shares in his evil deeds.

Where is the headquarters of the one true church?

Hebrews 12:22-24 But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, to an innumerable company of angels, (23) to the general assembly and church of the firstborn who are registered in heaven, to God the Judge of all, to the spirits of just men made perfect, (24) to Jesus the Mediator of the new covenant, and to the blood of sprinkling that speaks better things than that of Abel.
Ephesians 1:19-23 and what is the exceeding greatness of His power toward us who believe, according to the working of His mighty power (20) which He worked in Christ when He raised Him from the dead and seated Him at His right hand in the heavenly places, (21) far above all principality and power and might and dominion, and every name that is named, not only in this age but also in that which is to come. (22) And He put all things under His feet, and gave Him to be head over all things to the church, (23) which is His body, the fullness of Him who fills all in all.

How is it organized?

Ephesians 2:19-20 Now, therefore, you are no longer strangers and foreigners, but fellow citizens with the saints and members of the household of God, (20) having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone,

Who is to say that your discernment of organization is the correct one?

1 Thessalonians 5:21 Test all things; hold fast what is good.
2 Corinthians 5:10 For we must all appear before the judgment seat of Christ, that each one may receive the things done in the body, according to what he has done, whether good or bad.

Why is Jesus Christ the only way?

John 14:6 Jesus said to him, “I am the way, the truth, and the life. No one comes to the Father except through Me.
Acts 4:10-12 let it be known to you all, and to all the people of Israel, that by the name of Jesus Christ of Nazareth, whom you crucified, whom God raised from the dead, by Him this man stands here before you whole. (11) This is the ‘STONE WHICH WAS REJECTED BY YOU BUILDERS, WHICH HAS BECOME THE CHIEF CORNERSTONE.’ (12) Nor is there salvation in any other, for there is no other name under heaven given among men by which we must be saved.”
1 Corinthians 3:11 For no other foundation can anyone lay than that which is laid, which is Jesus Christ.

Are there further revelations than what was written some 2000 years ago and before?

Galatians 1:8-9 But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed. (9) As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed.
Jude 1:3 Beloved, while I was very diligent to write to you concerning our common salvation, I found it necessary to write to you exhorting you to contend earnestly for the faith which was once for all delivered to the saints.

What does your temple look like?

1 Peter 2:4-5 Coming to Him as to a living stone, rejected indeed by men, but chosen by God and precious, (5) you also, as living stones, are being built up a spiritual house, a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ.
1 Corinthians 3:16 Do you not know that you are the temple of God and that the Spirit of God dwells in you?

How can I join the one true church?

1 Corinthians 12:13 For by one Spirit we were all baptized into one body–whether Jews or Greeks, whether slaves or free–and have all been made to drink into one Spirit.