First theme, the journey of Christ's disciples to Emmaus: "Sweaty faces" , "If there were water we should stop and drink" , "Here one can neither stand not lie nor sit" , "Who is the third who walks always beside you?".
Second theme, the approach to the chapel: "Over the tumbled graves, about the chapel there is the empty chapel, only the wind's home".
Third theme, the present decay to Eastern Europe: "The awful daring of a moment's surrender which an age of prudence can never retract" , "each confirms a prison" , "London Bridge is falling down".

"The torchlight red on sweaty faces", "stony places", "frosty silence", "Here is no water but only rock", "Rock and no water and the sandy road", "rock without water", "Sweat is dry and feet are in the sand", "Dead mountain mouth of carious teeth that cannot spit", "cicada", "dry grass singing", "there is no water", "Over endless plains", "stumbling in cracked earth", "Ganga was sunken", "the limp leaves waited for rain".

Interpretation

The Thunder represent God's voice and his manifestation to men. In the Bible in fact God's is compared to a thunder. Furthermore, in this section, Thunder is also the advice to an imminent spring.

"These fragments" is referred to the present decay to Eastern Europe. The world in fact is fragmented and full of rubbish. There is only the hope of resurrection from this world of fragmentation and it will be possible to continue on despite the failed redemption.

The final message of the section and the poem is in non-western language (in Sanskirt) because even if the message conveys benediction and resignation, the solution is sought, it isn't got. People can't really go away from the waste land but there is only a hope. The same is for Western people.

I think Eliot's experimental poetry is very difficult to understand. To comprehend the whole significant you are expected to know all the past literature texts because Eliot's poems are made of intertextuality.

Eliot's poetry is full of intertextuality and references to other texts. So the obscurity is given by some past text you are expected to know to understand all the significant.

Read how Virginia Woolf described her own experience of reading Eliot:

Virginia Woolf underlines that Eliot's poetry is innovative and intense of beauty. She also said that is exiting the continuous passage to different texts of his lines (intertextuality) which is compared to a "spinning madly through mid-air".

Eliot, Woolf and Joyce are all Modernist writers who want the readers touch, feel, smell, see and taste their emotions. They use references to other texts and conveys feelings in innovative ways.