To compare these two poems is to compare the angelic and the miserable.  Both, of course, have to do with the service on Holy Thursday which needs a bit of explanation for most first-time readers.  In most cases, the Church of England considers Christ's Ascension day to be called "Holy Thursday," (although some insist that "Holy Thursday" can also be the day before Good Friday).  In any event, during the late eighteenth century (when the poem was written), the children from the charity schools of London were marched to a service at St. Paul's Cathedral. 

Blake's first "Holy Thursday" rightly belongs in his Songs of Innocence, for the children are seen as angelic:  they are "flowers" and "lambs," while with "radiance" they are "raising their innocent hands."  They were, of course, accompanied by the "beadles" who were instructed to enforce appropriate behavior.  The last line is meant to be a direct allusion to the thirteenth chapter of Hebrews that reads, "Do not forget to welcome strangers, for some have welcomed angels unawares" (Hebrews 13:2).  Angelic small children:  a cluster definitely belonging in the Songs of Innocence.

On the other hand, as with many of Blake's poems from his Songs of Experience, "Holy Thursday" focuses on the misery of the children involved.  Yes, it takes place on the exact same holiday (and perhaps chronicles the exact same service); however, unlike the angelic scene from Songs of Innocence, the speaker (although speaking of the land being "rich and fruitful") asks us a question regarding the misery of these children led to St. Paul's.  He asks if this is a holy thing to see these tiny children in their misery and hunger, led by beadles who rule over them harshly?  The speaker hears the children's "trembling cry" and is saddened at the knowledge that it's supposed to be a song and, at that, a song of joy.  No doubt, the children's great poverty is stressed in this poem.  In fact, by the second stanza the "land" has moved from being "rich and fruitful" to "a land of poverty."  By the third stanza, the poverty image is heightened.  The sun does not shine for these children.  The fields never yield a harvest for them and remain "bleak and bare."  Nature is full of hurtful "thorns."  The bleakness of winter is stressed as, for these poor children, "it is eternal winter there."  Finally, there is a reference to the aspects of life that the children are missing (and some say a description of the afterlife for them).  The speaker now speaks of a place where "the sun does shine" and where "the rain does fall" and where no child goes hungry.  This is a place where poverty does not abide.

Perhaps the last stanza of this final "Holy Thursday" brings the idea full-circle.  Perhaps the angelic quality from the Songs of Innocence can at least be imagined in this last stanza for the poor children of the Songs of Experience.  Although, I will admit, that is open to interpretation.