He Partha Sarathi is a favourite song of mine, and I know quite a few other students of Sri Chinmoy who like it very much too. It was written by Kazi Nazrul Islam, a famous Bengali composer. Partha Sarathi literally means charioteer of Arjuna, i.e Krishna, and the song reverberates with imagery taken from the Mahabarata, the famous Indian epic whose focal point is an all-consuming battle between light and ignorance. The opening lines invoke Krishna to blow his famous conch, Panchajanya. Conch shells were traditionally used at the start of Indian battles to summon men to arms, and the cacophony of conches would infuse the warriors with courage and strength for what would lie ahead.
However, the battle the poet refers to is the inner one - "Drive away this depression of the heart, make them fearless who are struck with fear", so the English translation goes, as the song exhorts each of us in the battlefield of life to leave behind human bondage and take shelter in the Divine.
The dynamic, inspiring tone of the song is typical of the songs that Nazrul used to write in the 1920's and 1930's. He saw himself as a rebel on many fronts against the imposing oppressions of the time. He fervently desired to end the British occupation of India, and for that he spent a year in jail and had many of his books banned.
He also was a firm opponent of religious narrowmindedness. He was brought up in a poor Muslim family, but at age 17 he joined the Indian Army and had his outlook widened by coming into contact with Persian and Hindu cultures. As He Partha Sarathi shows, many of his devotional songs use Hindu as well as Muslim means of religious expression. He recieved much criticism from Muslim and Hindu conservatives for falling in love with and marrying a Hindu girl, and return, he was vehement in his opposition to what he saw as unnecessary orthodoxy which hurt people more than anything.
If you want to find out more, heres a very nice Wikipedia article. Authors of most Wikipedia biographies tend to leave their own footprint on the article too much for my liking and this one is no exception, but this is probably the best biography I've read so far.