Why is believing correct doctrine so important? Simply put, because Jesus is the way, the truth and the life, no one goes to the Father except by Him (John 14:6). That in knowing the truth we are made free of sin (John 8:32 ff ). A doctrinal truth is a truth revealed to us by God through Jesus or the apostles. John 14:6 tells us that the only way to go to the Father who is in heaven is by the truth. Therefore through the truth is the only way to heaven. If we accept false doctrines we are decreasing our knowledge of the truth and we are therefore in real danger of turning away from the faith (1 Tim 4:1). That's why Paul reminds Timothy and Titus many times to confront those who teach falsely (1 Tim 4:16, 2 Tim 4:2, Tit 1:9). But in this day and age, where do WE go to have the truth? When one says that the consecrated bread and wine are mere symbols of His flesh and Blood and another believes that the bread and wine are actually His Flesh and Blood, Soul and Divinity…who do we believe? Who has the final say in determining the truth? Jesus instituted a final arbiter and defender of the truth which can decide infallibly what is true. Scripture plainly tells us that the defender and upholder of the truth, the last resort when searching for the truth, is the Church (Matt 18:15-17) and that is how the first followers of our Lord Jesus Christ understood the matter.
We know this because we see the first application of this teaching in the council of Jerusalem as found in the book of Acts (Acts 15:2, 15:28) who's decision was binding for all Christians (Acts 16:4). The trick now is to determine which Christian Church out of the thousands of Christian churches out there today, which one has been in existence from day one. This church is the one Church that Jesus tells us that we are to go to determine the truth with assurance since He promised that the gates of Hell would never prevail against His church (Matt 16:19). She therefore must be in existence throughout history from its inception to today so that we might go to Her to settle these issues as they did at the council of Jerusalem. Which Christian church out there claims to be 2,000 years old with evidence to back its claim? Only the Catholic Church can make that claim.