You don't need calc. Here's how I see it, take it for whatever it's worth.
All of the Bible is FOR us...for our learning from prior examples, for our instruction, encouragement and edification. All of it. Heir, Nick, STP -- no dispensationalist on this thread or on TOL will disagree with that.
But that does not equal all of the Bible being written TO us or ABOUT us. It is ONLY in the specific areas of Scripture written to and about us that we find what we need to know about the believer's identity, walk and destiny in Christ during this dispensation of grace.
As STP ably said, the problems arise when people do not distinguish between "for us" and "to/about us." That failure invariably makes utter confusion of Scripture, even to the point of creating what appears to be flat contradictions in God's Word where - if one simply looks at to whom, about whom or when something was written - no such conflict exists.
Put another way:
“It shall greatly help ye to understand Scripture if thou mark not only what is spoken or wrythen, but of whom and to whom, with what words, at what time, where, to what intent, with what circumstances, considering what goeth before and what followeth after."
Miles Coverdale
It's really that simple.
Now, most protestants/evangies/fundies will look at Coverdale's quote and say, "Oh, sure. I do that...Old Testament, New Testament...got it." But that is incomplete. They fail to RIGHTLY divide the Word in accordance with the divisions already placed in Scripture by God Himself. Simply saying OT/NT isn't it.