The phrase the straight and narrow means the honest and morally acceptable way of living.
The adjective strait is from Old French forms such as estreit (modern French étroit), meaning tight, close, narrow, from Latin strictus (cf. English strict), past participle of the verb stringere, to tighten, to bind tightly (cf. English strain and stringent).
One of the literal meanings of strait was, of a way, passage or channel, so narrow as to make transit difficult. This is why the gospel of Matthew, 7:13-14, a section from the Sermon on the Mount, is as follows in the Early Version (around 1382) of the Wycliffe Bible:
Entre ȝe bi the streyt ȝate; for the gate `that ledith to perdicioun, or dampnacioun, is brode, and `the weye large, and `ther ben many that entren bi it. How streit is the ȝate, and narewe the weye, that ledith to lijf, and `there ben fewe that fynden it.
In the King James Version (1611), these verses are:
Enter yee in at the strait gate, for wide is the gate, and broade is the way that leadeth to destruction, and many there be that goe in thereat:
Because strait is the gate, and narrow is the way that leadeth vnto life, and few there be that find it.
These verses are as follows in the New International Version (2011):
Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. But small is the gate and narrow the road that leads to life, and only a few find it.
The use of strait with reference to the Bible is found for example in a poem of Bel-vedére, or, The Garden of the muses (London, 1600), an anthology by the literary patron John Bodenham (circa 1559-1610):
No wise man likes in such a life to dwell,
Whose wayes are strait to heauen, but wide to hell.
In the current phrase, the straight and narrow (elliptical for the straight and narrow path, or way), straight is therefore an alteration probably due to misunderstanding or misspelling. In a spiritual context, straight (i.e. not crooked) makes nevertheless good sense in collocation with narrow.
The collocation has also been used to refer to the material world, as in The History of the Rebellion and Civil Wars in England (Oxford, 1717), by the English statesman Edward Hyde, 1st Earl of Clarendon (1609-74):
The Earl of Essex had but straight and narrow room for his Quarters for so great an Army of Horse and Foot.
More generally, much as purists may object, as strait became old-fashioned and unfamiliar, it was interpreted as the more usual word straight, as in straightjacket and straight-laced for straitjacket and strait-laced. (The word strait-laced means, literally, wearing stays or bodice tightly laced, hence, figuratively, having or showing very strict moral attitudes.)
In fact, the misspelling straight is not recent; for instance, the following is from The Surgeons Guid: Or Military and Domestique Surgery (London, 1658), by William Johnson (floruit 1658):
With hard binding the flesh is prest together, and is forced to cleansing, and weeping: and if it hath vent, it bleeds no more. This Symptom is thus remedied, to bind the wound slackly, and let the party not put on too straight [= tight-fitting] clothes.
The word strait survives as a noun, often in the plural with singular sense, in geographical proper names such as the Straits of Gibraltar, in which it denotes a narrow passage of water connecting two seas or two other large areas of water. The noun is also used in reference to a situation characterised by a specified degree of trouble or difficulty, often in the phrase in dire, or desperate, straits.
The phrase is sometimes used in the form the strait and narrow, for example in Secrets of a happy family holiday, published in The Telegraph (London) of 3rd June 2014, by Anthony Peregrine:
People are invariably astonished to learn that I am a grandfather. “Surely not?” they cry. “So youthful, so vigorous, such a glowing complexion! How do you do it?”
“E-numbers, mainly,” I reply. “I have handfuls with each meal. Cigarettes and whisky have also played their part.” This satisfies most enquirers, putting their own life-styles back on the strait and narrow, and leaves me free for grandfatherly duties.
In the French versions of the gospel of Matthew, 7:13-14, the formulation is la porte étroite, the narrow gate. La Porte étroite (1909 – translated in English as Strait is the Gate), by the French novelist, essayist and critic André Gide (1869-1951), is a novel about the failure of love in the face of the narrowness of the moral philosophy of Protestantism.
The French equivalent of to keep to the straight and narrow is rester dans le droit chemin, literally to remain in the straight path.
The French word étroit corresponds to English strait, which illustrates the fact that to many English words beginning with s- + consonant correspond French words beginning with é- (or, sometimes, es-) + consonant; for example:
– strange ↔ étrange
– school ↔ école (but there are words such as scolariser, to provide with schooling)
– student ↔ étudiant(e) (and the adjective estudiantin(e), as in vie estudiantine, student life)
– scale (graduated range) ↔ échelle
– scale (of a fish, of a reptile) ↔ écaille
– study ↔ étude (noun), étudier (verb)
– sketch ↔ esquisse
– spirit ↔ esprit
– scaffold ↔ échafaud
– scaffolding ↔ échafaudage
– spice ↔ épice
– spinach ↔ épinard
– slave ↔ esclave.