There are three prominent images in this poem: fire, water, and roses. All three should be examined closely for figurative and symbolic meaning.
Roses are a traditional symbol of English royalty, and this poem is no exception. Eliot is metaphorically speaking of all of England. But he is also drawing from the idea that roses represent growth, new life (as in the blossoms in Spring), as well as divine love and mercy. The spiritual element is carried out further with fire and water.
Fire is a common symbol in literature (and poetry) representing purification (refinement by fire), destruction (not necessarily negative), and eternal punishment (as in the fire of Hell). Fire is first introduced in the poem as in "frost and fire," meaning, the sun. In the rest of the poem, it is frequently paired with water, suggesting it is figuratively used to represent both the ideas of purification as well as damnation. "Pentecostal fire" (a Biblical image) is the suggestion of a supernatural and spiritual change. Later, however, the "communication of the dead is tongued with fire," suggests fire represents something eternal as well.
Finally, water, which is a common image used to represent growth or life movement (like rivers), change, and Baptism (as a spiritual cleansing). In this poem it is always paired with fire, and so provides a figurative balance between the dirty, harsh, or painful changes brought about by fire with the clean, calm, and soothing changes brought about by water.
As all Four Quartets focus on one of the four central elements of nature (earth, wind, water, fire), this, the last of the quartets maintains such natural imagery and figurative language in its pursuit to raise spiritual questions.