Devoutness, putting energy into compassion (5)
I believe the answer is:
piety
'devoutness' is the definition.
(I've seen this before)
'energy into compassion' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'into' means one lot of letters goes inside another.
'compassion' becomes 'pity' (pity is a kind of compassion).
'e' going inside 'pity' is 'PIETY'.
'putting' acts as a link.
(Other definitions for piety that I've seen before include "Devotion to religious principles" , "An unthinkingly accepted belief" , "Being faithful" , "Holiness" , "Attentive religious practice" .)