"Is the church really that important?"
Yes it is. The Bible speaks of but one church, the church of Christ (Ephesians 4:4; Colossians 1:18).Christ has promised to save His church at the Last Day (Ephesians 5:23). No salvation is promised to those out of Christ but instead they “shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power” (2 Thessalonians 1:7-9).
The Scriptures teach that the church is the body of Christ, and that each person has a purpose and is useful (1 Corinthians 12:12-18). All Christians serve the cause of Christ and are a part of the church He built, and are valuable no matter their age or gender (Galatians 3:26-29).
When Jesus came to earth, one part of His mission was to build the church (Matthew 16:16-18). Before Jesus ascended to heaven, Jesus gave a mission to the church, saying, "...Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, teaching them to observe all that I commanded you..." This has always been and continues to be the mission of the church.
Not only did Jesus build the church and give it a mission, but Jesus also died for the church (Ephesians 5:25). Since the church was this important to Jesus, it is important to us too.