What did siddharta mean by suffering is caused by the disire for material things and the only relief from suffering is living a religious life

You have to let go of material possessions in order for your mind to be free, when he says religious lifestyle he means one that is based on being one with nature and with the universe and with the self. To be kind to every soul that makes your way, and to let go of selfish desires. To appreciate every aspect of life.  This is what Siddartha meant, I reccomend you actually read the book, has a strong message.