There were many patriotic songs available that could have been considered for national anthem like Vande Mataram or Sare Jahan Se achha while deciding freedom, but Jana Gana Mana was adopted in view of its inclusive spirit and secular approach.
It does not refer to any religion, any region, or any caste.
The lyric itself is pan-Indian, speaking of all the states and cultures of India.
It has the prefixes of message of unity, peace, and common destiny of people in the nation.