From The Temple.
In the Latin alphabet here is no "J" and "I" is used instead. On public buildings, schools and government monuments, you often see "IVSTICE" [JUSTICE]. The poems on the back of the 1633 edition of The Temple are listed in alphabetical under with this poem appearing under "I." George Herbert takes this convention and sees "Jesu" as "IESU."
JESu is in my heart, his sacred name Is deeply carved there: but th’other week A great affliction broke the little frame, Ev’n all to pieces: which I went to seek: And first I found the corner, where was J, After, where ES, and next where U was graved, When I had got these parcels, instantly I sat me down to spell them, and perceived That to my broken heart he was I ease you, And to the whole is J E S U.