The spiritual body is developed through the practice of Krishna consciousness. This material body is spiritualized by this bhakti-yoga process. If you place an iron within fire, the iron becomes so hot that it also becomes fiery. When the iron is red hot, it acquires all the qualities of fire. If you touch something with that iron, that iron will act as fire. Similarly, although this body is material, it can become spiritualized through Krishna consciousness and act as spirit.
Reference: The spiritual body is developed through the practice of Krishna consciousness. This material body is spiritualized
