While Mennonites hold tightly to the belief that we are saved through God’s powerful gift of grace, we don’t subscribe to the “eternal security,” or “once saved, always saved” theology. And though we believe that we are ultimately saved by God’s grace, and not through any action or merit of our own, we also believe that maintaining a right relationship with Christ means that we are to follow in his footsteps and live a life that follows his example. Each member of the church has free will and can separate themselves from the body of Christ and live a sinful life, even if they once were bound to Christ. If that happens, the church will continue to pray for them and seek to restore them to fellowship, but the individual may still choose to forfeit his/her right to salvation.
For more discussion on the Mennonite view of eternal security see http://gameo.org/index.php?title=Eternal_Security