This is a series of lectures in English delivered in the United States and England in 1900 during Swami Vivekanda's international tour. 

The soul must be eternal. Why? In the first place we see that the soul is not matter. It is neither a gross body, nor a fine body, which we call mind or thought. It is neither a physical body, nor what in Christianity is called a spiritual body. It is the gross body and the spiritual body that are liable to change. The gross body is liable to change almost every minute and dies, but the spiritual body endures through long periods, until one becomes free, when it also falls away. 

When a man becomes free, the spiritual body disperses. The gross body disintegrates every time a man dies.