All the people who gather to worship in churches around the world form one body—the body of Christ. Jesus is the head. Paul described Him as "the beginning, the first-born from the dead" (Col. 1:18). He takes priority in the church and in the lives of every believer.
At salvation, you become a part of the body. By receiving the Savior, repenting, being baptized in Jesus’ name and receiving the gift of the Holy Ghost, a person is made one with Jesus. Therefore, if you're a believer, you are a breathing and active part of Christ, who is at work on earth through His followers. The church is Jesus' feet to carry the gospel message, His arms to care for those in need of love, and His hands to uphold the weak.
Christ's physical body underwent terrible pain and persecution. His church body cannot expect a cozy, easy existence either. Being Jesus to the world means making sacrifices, accepting ridicule, and loving our enemies (Heb. 13:16, Matt. 5:44). God called us to spread the gospel, but that doesn't mean people always like what we have to say. Sin and accountability aren't popular messages. Yet being trendy and well liked is not the point. We're here to carry out the work and mission of God, even when doing so is uncomfortable.
The spiritual makeup of the church is linked to its mission. The gospel cannot be spread except through the strength and wisdom of Jesus Christ, the head. The body of believers is united with Him through the indwelling presence of His Holy Spirit. He reaches the world through His church and its members.