Perhaps I am a slow learner, but it just occurred to me recently that the Calvinistic doctrine of eternal security, while germane to Calvinism, is not limited to a Calvinistic theology.  Even an Arminian could hold to the doctrine of eternal security (once saved always saved) while disagreeing with the Calvinists on the question of how people become saved.  Arminians could hold that it is impossible for someone whose spirit has been regenerated by the Spirit to fall away without accepting the Calvinist notion that God alone determines who will be regenerated.  The question of how we are saved (monergism or synergism) is separate from the question of the permanence of salvation.  It could be true that humans have to freely respond to God’s offer of grace before God saves them (synergism), and that once saved, a person will always persevere to the end.  There is no logical incompatibility between these two positions.