What follows is ONE of the proof texts which Calvinists frequently throw out for our consideration:
God plans our days before we are born, for David affirms, “In your book were written, every one of them, the days that were formed for me, when as yet there was none of them” (Ps. 139:16).
I took a look at this passage today. I discovered that there are alternate translations.
Thy eyes saw my substance, not yet formed; and in thy book all my members were written, which in continuance were fashioned, when as yet there was none of them. RWebster [bolding mine]
The Revised Webster gives a quite different slant on the passage. It is the body parts, the members, that were written in His book before they existed.
I also studied the passage in the Greek Septuagint (there are several different "versions" of the Septuagint as well. The Septuagint translation of the OT seems to be the one that the NT writers used. I have been wondering whether something has been omitted. It reads like this:
Your eyes saw the unworked of me, and all shall be written in your book (days) they shall be formed in you.
Now the problem is that "days" seems to be sitting in isolation. It is in the accusative case, which means that it is the object of a verb. But there is no verb for which it can be the object. So I'm guessing that there was once such a verb, but that scribes somehow failed to copy it into the text.
If "days" were the subject of the verb "shall be written", it would be in the nominative case.
addendum:
Okay, I've been a bit incomplete in my study of the verse. I took for granted that it was an accusitive plural, because books giving the analytical text stated so. But just now I remembered that the form can also be the
genitive singular. In that case the meaning is "of the day". So it would read, "...all shall be written in your book of the day..."
This would make sense. God was writing it in His day book.