Providence and Preservation (Ephesians 4:30 (COD Head 5 Article 6)

When we think about the Reformed doctrine of salvation we could think that the doctrine is simply summarized as such, “Once saved always saved.”  I have to confess that personally such a definition really bothers me.  It makes salvation sound cheap in the sense that we just go along for the ride and there is no struggle.  So, if this is not something I like then what can we put in the place of it?  What is more, how can Reformed people be so sure that God will preserve sinners who naturally hate Him?  How does the Spirit even work in Reformed theology?