Choose to study organ: be encouraged (4,5)
I believe the answer is:
take heart
'be encouraged' is the definition.
(I've seen this before)
'choose to study organ' is the wordplay.
I cannot really understand how this works, but
'choose' could be 'take' (synonyms) and 'take' is located in the answer.
'organ' could be 'heart' (the heart is an organ of the body) and 'heart' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for take heart that I've seen before include "Don't be discouraged - seek cardiac support (4,5)" , "Have courage, acquire cardiac boost" , "how to gain courage" , "to leave outside leaves of lettuce" , "Be encouraged or cheered up in cardiac way" .)