The universal church composed of God’s family—spread out among different local churches—is the one true church. Salvation comes through Jesus alone, but a church is “true” when its teachings and leadership align with God’s Word.
The New Testament defines the church in two distinct ways. First, the church comprises all believers—the universal church (John 10:16; Galatians 3:28; Revelation 7:9-10). Paul wrote letters in the New Testament to believers in many different areas, but they were all part of Christ’s “church.” The New Testament also uses the word church in the sense of a local group of believers who meet together to worship God; Paul refers to such local churches in his letters (1 Corinthians 1:2; 1 Thessalonians 1:1), and the apostle John distinguishes among seven specific churches in the first chapter of Revelation.
Both the local church and the universal church in these contexts are composed of the body of Christ and are, therefore, biblically considered the "true church.” We can figure out if the church we are attending is a “true” church if it is clearly following God’s Word (John 8:31; 2 Timothy 3:16-17; Acts 2:42).
"Which church is the true church?" The question is a good one, but the wide variety of churches today can make sorting out the answer difficult. A good start is thinking about what a “church” is not. The church is not a visible building or organization; it is the body of Christ. The church is also not one specific denomination as the Roman Catholic Church and the Mormon church claim to be. Protestants reject their claims of exclusivity and view the church as all people who have faith in Jesus Christ as lived out by their allegiance to His Word. But even among Protestant denominations, there is diversity regarding beliefs and practices.
Being a member of a Bible-teaching local church is important (Hebrews 10:25), but even more important is knowing we are born again (John 3:3; 2 Corinthians 13:5), new creations in Christ (2 Corinthians 5:17). No church can save us. Only Jesus saves, by grace through faith in His death and resurrection (Ephesians 2:8-9; Romans 10:9-10).