The word, 'sin' is a noun which means 'an immoral act/behaviour considered to be against divine law'. The word, 'vice' is a noun which means 'immoral or wicked behaviour'. As the two words are similar in meaning, option D, 'vice' is correct.
The word, 'purity' is a noun which means, 'freedom from adulteration or contamination'.
The word 'shield' is a noun which means 'a person or thing providing protection'.
The word 'secure' is an adjective which means 'certain to remain safe and unthreatened'.
As all the above three words are quite different in meaning from the word, 'sin', options A, B and C are incorrect.