wondering star, welcome to the forums.
You've asked a great question, this has been a matter of enormous controversy among Christians for about 500 years. The Apostle Peter rightly points out that there is much in the Bible that is difficult to understand, and warns of our tendency to deceive ourselves (2 Peter 3:16). That's why Jesus established a government in the hands of Church officers, giving it the authority to determine matters of controversy, so that when we disagreed in matters of doctrine we could go to the Church knowing that it would always teach the truth:
1. The church is a divine institution: the Bride and Body of Christ. ( Eph. 1:22-23; Song of Songs; Isaiah 62; Jeremiah 2:1-3; Jeremiah 3:1-5, 3:19-20, 5:7)
2. The church is the foundation and pillar of truth. (1 Tim. 3:15)
3. The Church is forever visible, not hidden. (John 1:3-5; Matt. 5:14-15; Luke 8:16,11:33)
4. The Church will proclaim the true gospel continuously, forever. (Isaiah 59:21; Matt. 16:18b; Matt. 28:20b; 1 Pet 1:25)
5. The Church is built on the foundation of the Apostles.( Ephesians 2:17-22; Ephesians 3:4-5)
6. Jesus will always be with the Apostles, and they will never teach erroneous doctrine. (John 14:16-17; 15:26; 16:12-13, 17:17-19.)
7. The Apostles speak with the authority of God. (Matthew 10:20, Luke 10:16)
8. The Apostles will remember everything Jesus taught them. (John 14:16-18, 26, Luke 21:33)
9. The Apostles will be one in the doctrine they teach. (John 17:20-23)
10. The Apostles have the power to forgive sin. (John 20:21-23)
11. God will give the Apostles whatever they ask for in Christ’s name, and the fruit they bear will remain. (John 15:16, 16:23; Romans 1:13)
12. St. Peter has a pre-eminent place among the Apostles. (Matthew 16:17-19; Isaiah 22:20-25)
13. The Apostles, and not the believers at large, had the authority to interpret Scripture and teach binding doctrine. (Rom 13:1-2; Heb. 13:17; 1 Tim 1:3; 2 Pet. 1:16–21, 3:2, 3:16; Jude 8, 10-11, Numbers 16)
14. The Magesterium (the teaching authority of Christ’s Church) exercised that authority to make binding decisions on matters of faith. (Acts 15)
15. The teaching authority that Jesus gave to the Apostles extended to the Apostles’ successors. (Acts 1:20,26; 2 Tim 2:2; 1 Cor 3:9-11)
This was always the belief and practice among Christians from the earliest days: go the the Church. We see this in Acts 15, when the first Church council determined the controversy about whether or not one had to be circumcised in order to become a Christian. Jesus hadn't told them the answer to that himself, if he had there would have been no controversy. He allowed the teaching authority of the Church, guided by the Holy Spirit, to determine the answer.
If you read the writings of the earliest Christians, you'll see that they believed that the Church had this authority. Read this, from Clement, 3rd Bishop of Rome, student of the Apostle Peter:
“Christ, therefore, is from God, and the Apostles are from Christ...Throughout the countryside they preached; and they appointed their earliest converts, testing them by the spirit, to be the bishops and deacons of future believers...Our Apostles knew through our Lord Jesus Christ that there would be strife for the office of bishop. For this reason, therefore, having received perfect knowledge, they appointed those who have already been mentioned, and afterward added the provision that, if they should die, other approved men should succeed to their ministry...Shameful, beloved, extremely shameful and unworthy of your training in Christ, is the report that on account of one or two persons the well-established and ancient Church of the Corinthians is in revolt against the presbyters. And this report has come not only to us, but even to those professing other faiths than ours, so that by your folly you heap blasphemies on the name of the Lord, and create a danger to yourselves...If anyone disobey the things which have been said by Him through us, let them know that they will involve themselves in transgression and in no small danger. We, however, shall be innocent of this sin...” Letter to the Corinthians (AD 80)
Or this from Ignatius, 3rd Bishop of Antioch, student of the Apostle John:
“It is necessary, therefore, -and such is your practice, -that you do nothing without the bishop, and that you be subject also to the presbytery, as to the Apostles of Jesus Christ our hope...In like manner let everyone respect the deacons as they would respect Jesus Christ, and just as they respect the bishop as a type of the Father, and the presbyters as the council of God and the college of Apostles. Without these, it cannot be called a Church...anyone who acts without the bishop and the presbytery and the deacons does not have a clean conscience.” Letter to the Trallians (AD 110)
“For Jesus Christ, our inseparable life, is the will of the Father, just as the Bishops, who have been appointed throughout the world, are the will of Jesus Christ. It is fitting, therefore, that you should live in harmony with the will of the Bishop - as indeed you do...Let us be careful, then, if we would be submissive to God, not to oppose the Bishop. Furthermore, the more anyone observes that a Bishop remains silent, the more he should stand in fear of him. For anyone whom the master of the house sends to manage his business ought to be received by us as we would receive him by whom he was sent. It is clear, then, that we must look upon the Bishop as the Lord Himself...” Letter to the Ephesians (AD 110)
“You must all follow the bishop as Jesus Christ follows the Father, and the presbytery as you would the Apostles. Reverence the deacons as you would the command of God. Let no one do anything of concern to the church without the bishop.” Letter to the Smyrneans (AD 100)
“I exhort you to be careful to do all things in the unity of God, since the bishop sits in the place of God, and the presbyters in the place of the synod of the Apostles, and the deacons, who are most dear to me, have been entrusted with the ministry of Jesus Christ, who was with the Father before the world began, and was manifested in the end...Be diligent, therefore, to be confirmed in the doctrine of the Lord and of his Apostles, that ye may be prosperous in all things, whatsoever ye do, both in flesh and spirit, in faith and love, in the Son and the Father and the Spirit, in the beginning and the end, together with your most worthily-distinguished bishop, and the nobly woven spiritual crown of your presbytery, and of your deacons, who walk according to God. Submit yourselves to your bishop and to each other, as Jesus Christ to his Father according to the flesh, and the Apostles to Christ, and to the Father, and to the Spirit; that there may be a union both fleshly and spiritual.” Letter to the Magnesians (AD 110)
“Abstain from evil herbage, which Jesus Christ doth not cultivate, because it is not the planting of the Father. Not that I have found division among you, but thorough purity.I cried while I was among you, and spake with a loud voice, saying, Give heed unto the bishop, and to the presbyters, and to the deacons. But they suspected that I spake these things because I knew beforehand the division of certain of them; but he, for whose name I am in bonds, is witness unto me that I knew not these things through the flesh of man. But the spirit preached, saying these things: Do nothing apart from the bishop; keep your flesh as the temple of God; love unity, avoid divisions; be imitators of Jesus Christ, even as he is of his Father.” Letter to the Philadelphians (AD 100)
The idea that every Christian has the authority to decide for himself what the Bible teaches, without having to bother with what is taught by the Church, is a modern invention that isn’t supported either by the Bible itself or the evidence of history.
The Church also exercised that authority in the councils that answered the great heresies: Gnosticism, Montanism, Sabellianism, Arianism, Pelagianism, Nestorianism. Monophytism, Iconoclasm... Mind you,
every heresy was touted by those who claimed to find support for it in Sacred Scripture. Is Jesus God, or merely a creature? If he only human, or only divine, or both? Are Jesus and God the Father two distinct persons, or merely different modes of the same person? Do we inherit original sin? Can we reach out to God under our own power? Even the question about what books should be recognised as Sacred Scipture was answered by councils of the Church.
When these questions were decided by the Church, no one argued about them any more until recent times. But now there are again people who claim to be Christians but who also hold to one or other of the great heresies. The reason for it is that they reject the teaching authority that was established by Christ, believing that all they need is the very Bible which says that they need more than just the Bible. And so you’ll get nearly as many answers to a question as there are people of whom you can ask it.
Some people will tell you that Christians agree on the essentials, and disagree on non-essentials. But the problem is that the question of what is essential and what is non-essential, is itself an essential matter. And then they'll turn around and call someone's salvation into question on the grounds that they don't agree with them on some matter. Heck, at least one Christian denomination has officially said that we can't decide whether or not it's wrong to kill an unborn child, so everyone needs to figure it out for themselves! That's not an essential matter? - who is and who is not a person?
So who do you ask for help? The teaching authority that was established by Christ. In which Church do we find that authority? Easy: the one that has existed since the beginning of Christianity.
