What features make murder in the Cathedral a poetic drama?

The title itself implies that there is a dramatic story to this. Elliot combined his genius of poetry with drama to create this famous work. Most of the characters speak in verse giving the play a vert lyrical flow as well as intense tone. The vivid imagery is filled with alliterations, staggered rhyme schemes and bright personification. This is all the stuff of great poetry embedded into a consistent plot.

What features make murder in the Cathedral a poetic drama?

Eliot sought to combine his poetic talent with the form of drama in this excellent and outstanding text. It is easy to see the massive influence that poetry has on this play, as there are only two sections that are written in verse, which are Thomas's Christmas sermon and the so-called "apologies" of the Knights to the audience. The title itself implies that there is a dramatic story to this. Elliot combined his genius of poetry with drama to create this famous work. Most of the characters speak in verse giving the play a vert lyrical flow as well as intense tone. The vivid imagery is filled with alliterations, staggered rhyme schemes and bright personification. This is all the stuff of great poetry embedded into a consistent plot.
English poetic drama in the twentieth century arose as a reaction to the deteriorating naturalistic prose plays of Ibsen, Shaw and Galsworthy. Its photographic realism failed to convey the tension and complexity of contemporary life. Stephen Phillips perhaps initiated the revival of poetic drama with Herod (1901), with great Irish writers like Yeats, Synge and O'Casey later reinforcing the movement. Eliot took to writing plays late while already enjoying colossal poetic fame. Also a mature critic, he was well acquainted with the nature of poetic drama, its failure in the nineteenth century, and the problems, technical or otherwise, that a verse dramatist might face in his time. Through his criticisms, he frequently advocated for the poetic drama and crossed the misconceptions about it. In Matthew Arnold's words, he created "a current of fresh ideas" to help it flourish.
"The craving for poetic drama is permanent in human nature", Eliot once remarked. He knew that it was still possible in the twentieth century, only "it cannot be the work of one generation working together, but has to evolve by the small contributions of a number of people in succession, each contributing a little." He placed a high ideal of poetic plays before his age, beginning with Murder in the Cathedral, for which he did a lot of experimentation.
First, he asserted that "no play should be written in verse for which prose is dramatically adequate." Clearly, the poetic drama needed to symbolise the emotional realities, in contrary to the socioeconomic issues that constituted the naturalistic plays. In Murder in the Cathedral, he chose to retell the inner conflict of Becket to win over temptations and be a martyr by losing "his will in the will of God". The Family Reunion, on the other hand, deals with the guilt complex of the protagonist, while The Cocktail Party examines personal inadequacies of married life in the modern context. These plays demonstrate religion as the ultimate meaning of human existence, leading people "to think in Christian categories." As David Jones puts it, Eliot was thus "contributing to the creation of the kind of wholeness of outlook without which the poetic drama cannot be accepted as the normal mode of drama."
Poetic drama still needed a suitable verse form, as the Elizabethan blank verse became cliché in excessive use. Also a poetic drama written on the same theme, Tennyson's Becket tried to be Shakespearean and met an even worse reception than its predecessors. Murder in the Cathedral marks the maturing stage of Eliot's experimentation with verse forms, culminating in The Family Reunion. Nevertheless, the author was not much pleased with his structural achievement in the first play: "it succeeded in avoiding what had to be avoided, but it arrived at no positive novelty." The language of Murder in the Cathedral combines the metre of Morality Plays like Everyman with Laforgue's 'Vers Libre'; it is almost like a mantra, incantatory and biblical; harmonised perfectly with its Christian theme. Some of the best poetry comes with the Chorus, as in Part I:
"Here is no continuing city, here is no abiding stay.
Ill the wind, ill the time, uncertain the profit, certain the danger.
O late late late, late is the time, late too late, and rotten the year;
Evil the wind, and bitter the sea, and grey the sky, grey grey grey."
This artistic repetition resounds the famous lines in The Waste Land: "Drip drop drip drop drop drop drop", or "Twit twit twit / Jug jug jug jug jug jug". According to Chinmoy Guha, these are further influences of Laforgue on Eliot. This is rather dramatic poetry than poetic drama. In Part II the Chorus cries: "Clean the air! Clean the sky! wash the wind! Take stone from stone and wash them. The land is foul, the water is foul, our beasts and ourselves defiled with blood.
A rain of blood has blinded my eyes."
The failure of the poetic drama in the bygone centuries chiefly rooted from its focus on outward decorations. Poetry must not be an embellishment to look at, but a medium to look through. Eliot distinguishes between true and false rhetoric, saying that the latter spoils the dramatic detachment of the audience. Poetry in Murder in the Cathedral is not merely decorative. It helps revealing the personae of the characters as the objective correlative of their minds, while its symbolism works out the thematic implications. Its long speeches indeed shine with rhetoric but at the same time build up the mood, the opening choric speech being a good example.
Eliot emphasised that instead of limiting the emotional range, the use of verse enlarges the appeal of the play, and can reach the most varied audience: "For the simplest auditors there is the plot, for the more literary the words and phrasing, for the more musically sensitive the rhythm, and for auditors of greater sensitiveness and understanding a meaning which reveals itself gradually." Like the successors to follow, Murder in the Cathedral unquestionably enjoys this wide range of possibilities.

Requited