The spirit of

Under Rajkumar Hirani's light touch and unwavering optimism, the darkness of Sanjay Dutt's life acquires the spirit of a sportsman, grit of a soldier, humour of a rascal and regrets of a son, notes Sukanya Verma.

https://m.rediff.com/movies/review/sanju-review-tears-cheers-bias-and-a-brilliant-ranbir/20180629.htm

Please explain the use of "the" before "darkness of.., spirit of..." and "a" before "soldier, rascal and son"