Spiritism is a religion but not in the traditional sense of what Religion stands for. Religion is usually associated with rituals of all sorts such as: worshipping with singing, prayers in a specific physical position, lighting of candles and incense, hierarchy of commands based on a central figure, devotions to spiritual entities represented in statues, money collection and so on…In that sense Spiritism is not a Religion because it doesn’t have any rituals. If you were to attend a Spiritist Center you wouldn’t find any of the rituals associated with traditional Religions.
Another important point is that, at first, a person new to Spiritism may have the impression that Spiritists worship Allan Kardec as a prophet of some sort. And that is not true at all. For the Spiritists, Allan Kardec was basically an instrument of the Enlightened Spirits as well as all the Mediums and the Spirits who were involved in the compilation of Spiritism. Allan Kardec is the codifier of Spiritism, in other words the organizer or the editor in chief of Spiritism and Jesus Christ is the highest moral model and guide to be followed.
Nonetheless Spiritism is a Religion according to the original definition of the word religion, which is to connect the creature with the creator. Spiritism is a Religion because it has the foundation of all Religions; the existence of God, the immortality of the soul, the consequences of our actions. Spiritism is a Religion because it brings back the Moral teachings of Jesus Christ free from allegory and dubious interpretations. Finally Spiritism is a Religion mainly because it leads individuals to better themselves thus connecting them with the Creator which is the pursuit of all Religions.