What you are talking about is Antinomism...(eating it too)
Calvinists take the word of God at it's word..He (Christ is the author and finisher of our faith.
We do not believe "once saved always saved" (that once saved you can do anything without fear of "losing your salvation" That would be a heresy)
We believe in the preservation of the saints..that is what we can not do ourselves ( grow in grace and persevere till the end) Gods grace can and will do as he is faithful and HE will not lose one that the father has given Him