Eastern male messenger casting the first stone (7)
I believe the answer is:
'first stone' is the definition.
'emerald' can be an answer for 'stone' (type of gemstone). I am unsure of the 'first' bit.
'eastern male messenger casting' is the wordplay.
'eastern' becomes 'eme' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'male' becomes 'he' (he refers to a man).
'messenger' becomes 'herald' (herald is a kind of messenger).
'casting' suggests deleting specific letters (as in casting away).
'herald' with 'he' taken away is 'rald'.
'the' acts as a link.
Can you help me to learn more?
(Other definitions for emerald that I've seen before include "Gem; type of moth" , "city in Oz?" , "Small size of type, in printing" , "Green - jewel" , "Bright green colour" .)