By resetting the castsequence on target it kind of negates the whole "renew if weakened soul".
Plus you haven't set a modifier ...

and that many renews is overkill.

AND!
This should work, i think.
Depending on how you have your macros set up, you might need one for each target character.

/castsequence [target=whatever you use] reset=15 Powerword: Shield, Renew, Renew, Renew
Maxion already posted it