Lamp is lit by holy person, one who praises God? (8)
I believe the answer is:
psalmist
'one who praises god?' is the definition.
(psalms are songs of worship)
'lamp is lit by holy person' is the wordplay.
'lit' indicates anagramming the letters (lit can mean drunk).
'by' is a charade indicator (letters next to each other).
'holy person' becomes 'st' (short for saint).
'lamp'+'is'='lampis'
'lampis' anagrammed gives 'psalmi'.
'psalmi'+'st'='PSALMIST'
(Other definitions for psalmist that I've seen before include "Old religious writer" , "David, most likely" , "Writer of sacred songs in Old Testament" , "Singer of sacred songs" , "poetic king ..." .)