I'm a monotheist that's spiritist, God blessed me with the gift of allowing me to talk to the spirits of the dead, so, i got an Ouija table and when someone needs help or wants to talk with someone they loved that has passed away, but i always advise that sometimes some lower level spirits try to pretend that they are someone else.
Certain times i make sessions alone to ask about the universe, and other philosophical matters, i have leurned that if you ask materialistic questions they wont give you much importance and lower levels may play a trick on you.
No, we don't have an holly book and our Church/mosque/sinagoge is the universe, there's no convertion or or disconvertion, you'll be a monotheist when you feal it in your heart, but that doesn't mean that monotheists are the holders of trueth, we are all humans so we also have imperfections but the main thing is, Do unto others what you would like they do to you, i'll give you a link that will help you understand better.

http://www.spiritwritings.com/kardecspiritstoc.html

Only God Can Judge Me
الله فقط يمكنه محاكمتي

I am you and you are me, if you love i love, if you suffer i suffer
أنا أنت, و أنت أنا, إذا أحببت نفسك أحببت نفسي, إذا عانيتَ عانيتُ