The “Infinitely gentle Infinitely suffering thing” Eliot refers to is his imagination that is bombarded by the images of the suffering of man.  Eliot explains he is twisted by the images of  his imagination.  He describes man’s suffering as : His soul stretched tight across the skies/That fade behind a city block,  which is possibly  a result of the industrial revolution that spawned the creation of towering buildings that engulfs man into obscurity,  Or trampled by insistent feet/At four and five and six o’clock  which suggest the death of man because he becomes a cog in the machine that powers modern society and also as: And evening newspapers and eyes/ Assured of certain certainties that suggest the blinding of propaganda and misinformation.  This stanza foreshadows the death of man.