(Reference text: T. S. Eliot Selected Poems, Introduction & Notes by Vasant A. Shahane; Penguin Critical Guides)
"'The Fire Sermon' was preached by the Buddha against the fires of lust and other passions that destroy people and prevent their regeneration" (see Norton Anthology, pg. 2375, footnote). The title of section 3 has been taken from the Buddhist philosophy. In fact, the implicit theme in section 3 also is connected with the above notion. In lines 175-79, Eliot cites the source in the refrain of the nuptial song in Prothalamion by Spenser, where Elizabeth & Katherine Somerset, daughters of the Earl of Worcester were being married & the nuptial song was composed for the event. The decorated river Thames at that time is completely contrasting image to the present one. In modern England, Thames is intoxicated not only by the tars & oil of the ships, but also by the illicit love-making of the young couples on the boats. The pollution of the river stands for degeneration of spirituality. As the speaker stands on the bank of Thames, he can hear noise of London crowds, motor horns, men calling girls for making love. Fishing, in Arthurian Legend, means salvation & eternity, but here, Eliot's spokesperson faces an ugly rat instead of finding fish, this reminds of the story of Ferdinand where the king was exiled by his brother. The real king can be compared to fish & the usurper can be with the rat. The song of nightingale which appeared to be sweet & innocent in early days, now, reminds people of sexual pleasure. Innocent is no more innocent in the eyes of the modern people since their perspectives have changed. In this section, the speaker makes us introduced with the Smyrna merchant whose pocket is full of samples of currants & documents. He stays at the Cannon street Hotel & spends the weekend at Metropole Hotel both of which are notorious for perversions & homosexuality. The merchant only knows money & lust.In the section 3, we are directly connected with Tiresias who can see everything, knows everything, but can't tell anything. He is a silent observer in the scene of the love-making of the carbuncular & the typist girl. While making love, the girl remains feelingless just like a robot as if it were her daily job; and it indicates that sex, in modern age, has become too mechanical & lifeless to enjoy. She seems to be "glad" when "it's over". In sex, only lust dominates, a little love prevails there now. The scene, later, shifts to the statements of the daughters of Thames, who poignantly describes the assaults perpetrated on them. Then, the speaker utters that, London has become like Carthage burning in the fire of lust. Carthage, by St. Augustine, was called cauldron of sensuality & he prayed to God for His Grace. As the title suggests, 'The Fire Sermon' refers to universal flame of sex which is becoming uncontrolled & burning the entire world gradually. The remedy is, according to both the Eastern & Western philosophy, to control lust & maintain discipline.
Buddha's wheel of Dharma and the Smyrna merchant also appears in the tarot cards through which madame Sosostris tells fortune in section 1.
Most importantly, Tiresias is an interweaver among all the incidents depicted in the poem. He's a unifier. The Smyrna merchant is an instrument used by the poet to portray the problems of modern age. And Buddha has been brought in order to connect his philosophy with the intricate problems, to show that, the problems are universal, not individual, and to pave way to a solution combining the Eastern philosophy with the Western one. This is how they are related in the poem. The internal theme or message, shifting of perspectives & dividing the poem into five sections have made the task of relating them with one another easier.