That does not teach OSAS, unless you believe that humans are puppets or automatons with no will.
Yes, you are sealed when you believe, and if you finally and impenitently turn away, you break the seal, as the scriptures teach. I don't like to proof text, but others don't seem to mind it.
Don't Calvinists find it strange that there is virtually no evidence for the Calvinist distinctives prior to Calvin? Or maybe Calvinists could point out where those distinctives were taught before the Reformed tradition sprang up. And saying "the Bible" is not sufficient because there are just as many places where the Bible contradicts those distinctives. That being the case, one must look to the earliest churches to see what was taught -- and it wasn't Calvinism.
Be very careful that you do not fall into those that Peter refer to here in
2 Peter 3:16
New International Version (©1984)
He writes the same way in all his letters, speaking in them of these matters. His letters contain some things that are hard to understand, which ignorant and unstable people distort, as they do the other Scriptures, to their own destruction.
New Living Translation (©2007)
speaking of these things in all of his letters. Some of his comments are hard to understand, and those who are ignorant and unstable have twisted his letters to mean something quite different, just as they do with other parts of Scripture. And this will result in their destruction.
English Standard Version (©2001)
as he does in all his letters when he speaks in them of these matters. There are some things in them that are hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other Scriptures.
New American Standard Bible (©1995)
as also in all his letters, speaking in them of these things, in which are some things hard to understand, which the untaught and unstable distort, as they do also the rest of the Scriptures, to their own destruction.
