Imagine the year, oh, 500 A.D. You’re a laborer hard at work building some glorious cathedral for the glory of God. Suddenly, because you’re thinking of meeting some buddies after work for a bottle of mead instead of focusing on what you’re doing, you slam a hammer into your thumb. “Oh for Chr-” you start to yell, cursing your stupidity, then notice the supervising priest staring suspiciously in your direction, and change mid-curse to “Oh, for Saint Peter’s sake!” said in an appropriately worshipful tone. The priest nods sagely and continues on his supervisory way.
Fast-forward a thousand years or so. The laborer’s great-great-great-ad infinitum grandson hits his thumb with his hammer and wonders why he takes 35 seconds yelling “Oh for Saint Peter’s sake” and shortens it to “Oh for Pete’s sake!” because there’s no priest watching.
Fast-forward to modern times. We have now labeled this phenomenon, because we must label everything so it can be analyzed to death. “For Pete’s sake” is a “minced oath,” a substitution of a less offensive word in a phrase. Which probably explains why few people say it anymore, because few people actually care about the offensiveness of their language today. And we have no priests supervising us who would string us up by our toenails and force us to recite the rosary 100 times upside down for taking the Lord’s name in vain.
And that’s where the phrase “For Pete’s sake” came from. Don’t you feel smarter now?