I like to think of Spells as a practical working of a Prayer. The items used within the process of casting a spell are used as aides to focus the thoughts and power.

The items do not cause the spell to happen, they are there to help the petitioner ask the divine to help him/her to achieve their goals, A spell is not necessarily unsucessful, it may be that a higher power has decided that it is not the right thing to happen at that moment in time.