As He was ready to ascend back to Heaven, following His resurrection from the tomb, Jesus told the apostles, "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you" (Matthew 28:19-20). How were the apostles to "make disciples of all the nations"?
The apostle Paul stated that God's plan is that we employ that same teaching method instructed by Jesus, namely preaching, "to save those who believe" (1 Corinthians 1:21). Paul wrote to the Colossians, "Him we preach, warning every man and teaching every man in all wisdom, that we may present every man perfect in Christ Jesus" (Colossians 1:28). What is God's plan for bringing sinful mankind to salvation? Teaching!
Some would probably still try to distinguish between teaching the gospel and teaching doctrine. But what does the word doctrine mean? Teaching. What did Jesus instruct to be taught in order to "make disciples of all the nations"? First, the gospel, and then "all things that I have commanded you" (Matthew 28:19-20). In his first letter to Timothy, Paul equates "sound doctrine" with "the glorious gospel" (1 Timothy 1:10-11). From that text we can conclude that without sound doctrine there would be no gospel.
One of the most pointed texts emphasizing the importance of getting doctrine right is found in John's second letter: "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" (2 John 9). As already noted in Jesus' instruction to the apostles at His ascension, the doctrine of Christ includes the doctrines by Christ (Matthew 28:19-20). Does doctrine matter? Only if you want to go to Heaven...