Gandhi himself called satyagraha as active resistance. Because even though satyagraha is not a physical force, it is a pure soul-force. According to him, if the cause was true and it involves struggle against injustice, then physical force is not required to fight the oppressor.
The idea of satyagraha involves the power of truth and the need to search for truth.
According to Gandhi, a satyagrahi could win the battle without being aggressive, through the power of truth. He believed that this non-violence method was going to unite all Indians in their struggle against the British.