Where does the phrase........

[Mr Tall]

Keep you on the straight and narrow come from?

[Clanad]

Most likely from "Enter at the straight gate: for wide is the gate, and broad is the way, that leads to destruction, and many there go in there: Because straight is the gate, and narrow is the way, which leades unto life, and few there be that find it' (Matthew 7:13,14). (Paraphrased)

[jno]

just a guess, but that might once have been 'strait', meaning restricted, as in straitjackets (which restrict people), strait of water (a narrow stretch), straitened circumstances etc; so it wouldnt necessarily mean 'not winding'.

[purplecarrot]

I agree with Clanad. I am religious and the scriptual text quoted is right in the nose. Just basically means to keep to a strict/correct way of life. Have no idea what on earth the other thing is regarding straight jackets??? sounds like he needs to be in one.

[jno]

why, thank you, purple carrot. I was trying to explain that the phrase was possibly once 'strait and narrow' and so it meant a restrictive and narrow road rather than a direct route from A to B, which is what 'straight' would mean.

So it's straitjacket. Not straightjacket. And I am not disagreeing with Clanad.

[Clanad]

Actually, jno you're probably not far off... the rendering in the original King James is strait... I didn't take the time to check my Concordance, but your interpretation related to updated translation probably includes your suggestion... in my opinion... By the way, please feel free to disagree with me any time!