Identifying with a local church is an expression of who Christ made us to be. The day we became Christians, we became part of the body of Christ and a member of God's family. When believers are not members of a local church, the body is incomplete and those believers are like estranged family members.
God designed the church to be a place for believers to find community and encouragement as we serve each other, grow together in Christ, and guide others to faith in Christ. It will be difficult to thrive in our relationships with Christ if we have a casual relationship with His church.