To be on the same page is to be thinking or understanding an issue similarly, or in agreement, though not necessarily on every detail. It is usually said about efforts to solve a problem.
Knowyourphrase.com says the origin is may refer to students opening their textbooks to the same page, or choral singers opening their music. That sounds plausible but sometimes people simply make up good stories to explain a phrase.
If the phrase seems to be recent, so Know Your Phrase may have found the origin in 1974, in the Corona Daily Independent:
“I think we can beat Washington and whichever [football] team we play next to get into the Super Bowl. If 47 players and our coaches are all on the same page, we can do it.”
Wherever it came from, tweakyourbiz.com calls this a business cliché, “a handy crutch when you’re groping for a word in a pressurized situation.” Perhaps some original thinking would lead to fresh language.
This phrase refers to attempts to convert someone who is already a believer – that is, a waste of time. According to Phrase Finder, this is a fairly recent phrasing, originating in the United States, based on an older version.
The first reference is from The Lima News, Ohio, January 1973:
“He said he felt like the minister who was preaching to the choir. That is, to the people who always come to church, but not the ones who need it most.”
An earlier English version dates back around a century further and is first cited in a letter to The Times in November 1857:
It is an old saying that to preach to the converted is a useless office, and I may add that to preach to the unconvertible is a thankless office.
It was subsequently made popular by John Stuart Mill.
The expression means to upset someone’s carefully made plans. According to Dictionary.com the expression has been around since the late 1700s, although there are references to similar Roman expressions.
The Phrase Finder explains that the this expression means to “Reprimand rowdy characters and warn them to stop behaving badly.” It had its origin in the actual English Riot Act of 1715. Any group of twelve or more unruly citizens had an hour to disperse or be arrested after the Riot Act was read to them. The English government was especially fearful of Jacobite mobs who wanted to overthrow the King and restore Roman Catholic Stuart King James VII of Scotland to the throne.
When recommending someone avoid rushing into an activity, we still say “Hold your horses.” This is a modern spelling of the idiom. As Wikipedia says
“Hold your hosses” (‘hoss’ being a US slang term for horse) appears in print that way many times from 1843 onwards… The first attested usage in the idiomatic meaning [came] from Picayune (New Orleans) in September 1844, “Oh, hold your hosses, Squire.”
The literal meaning is older:
In Book 23 of the Iliad, Homer writes “Hold your horses!” when referring to Antilochus driving like a maniac in a chariot race.
It seems strange that the idiom has survived the arrival of motorized vehicles, but there is a modern variation: cool your jets, which Stackexchange says originated in the US and was first quoted in a newspaper:
1973 Daily Tribune (Wisconsin Rapids) 29 Jan. 1/1 If you want to cool your jets, just step outside, where it will be about 10 degrees under cloudy skies.
The expression refers to revealing a secret, and Snopes says it originated from “. . .chicanery practiced upon those purchasing livestock.” An unscrupulous seller would swap a cat for a pig that had been purchased. The buyer wouldn’t know he had been duped until he returned home and “let the cat out of the bag.” The expression “Pig in a Poke” was posted earlier, and it had a reference to this expression.
Searching for the origin of this expression led me to two of my favorite sources. The Phrase Finder quoted Charles Earle Funk’s wonderful book, A Hog on Ice & Other Curious Expressions. “This may be jocular or serious; one is sometimes taken for a ride when he suffers nothing more than being kidded, made the butt of some joke. But in a sinister and the original sense the person taken for a ride rarely returns. The expression was of underworld origin, coined in the United States during the wave of criminality after World War I, when rival gangs of law-breakers waged warfare on each other. Anyone incurring the displeasure of a gang chieftain was likely to be invited to go for a ride in the car of the latter, ostensibly to talk matters over and clear up the misunderstanding. The victim rarely returned from such a trip. . . .”