One admitted to plead at the bar; one who has been “called to the bar.” The bar is the rail which divides the counsel from the audience, or the place thus enclosed. Tantamount to the rood-screen of a church, which separates the chancel from the rest of the building. Both these are relics of the ancient notion that the laity are an inferior order to the privileged class.
A silk gown or bencher pleads within the bar, a stuff gown or outer barrister pleads without the bar.
The whole society is divided into three ranks: Benchers, Utter Barristers, and Inner Barristers.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894