Translation:To help one's neighbors is a good deed.
Is this use of the reflexive pronoun with an understood subject covered somewhere in the notes? This is the first I've seen it. Seems pretty nuanced to introduce here without explanation.
Why is it sia? You don't know who's neighbour it is good to help. It could be if just his neighbour is helped that's good
Doesn't "si" require a subject to refer back to?