。
Helping a blind person is a kind act.
Literal
Blind-person [to-に] hand [object-を] lend-[nominalizer-の] [topic-は] kind act is.
手を貸す ('to lend a hand') is the standard idiom for 'to help, offer assistance,' exactly paralleling the English. 親切な行為 ('a kind act') is a plain noun phrase with the na-adjective 親切 modifying the noun 行為 ('act, deed') via the な link. The clause-level nominalization with の lets 'lending a hand to a blind person' act as the topic.