they are different almost all the time,while some universes have an exception where they may be the same we are going with the theory that the one we are talking about is not that case.  The one that we are basing this theory on is undertale au's and also the darkness of insanity universe. While the soul is the very culmination of your being which means its the thing that lets your body exist. basically if your soul exists then your body exists but once your soul is destroyed your physical body is gone. Your spirit is what forms your spiritual self/body/entity which exist in the spiritual plane of existence. NOT in the physical realm unless somehow you are a "ghost" after you die. which is an example of a unnatural occurrence where your spiritual self takes control of your soul, until you are able to pass on by completing unfinished business as a ghost. the reason it takes control over your soul is so your ghost/spiritual self can be seen after death and interact with the physical realm, but like i said it is an unnatural occurrence as well as a uncommon occurrence in these universes. Although thats not always the case in others... this is my theory on the difference of soul and spirit let me know what you think.