For as long as people have believed in angels, there has been people trying to summon these beings into their own lives. In fact, in Gust David son's Dictionary of Angels for example, most of the listed angels are from texts denoting spells and rites designed to call forth the residents of Heaven. Evocations are spells designed to cause a physical manifestation of the angel in the proximity of the summoned. Depending on the spell used, different components may be utilized including knives, circles drawn upon the floor, candles, books, incense, etc. The use of incense is particularly common since it is believed that the ethereal smoke is required as a body in which the angel may make itself seen.
Invocations are much like evocations with one major difference.
Instead of causing the angel to appear physically, the user of the magic tries to convince the angel to enter their body directly and thusly communicate with them that way. Needless to say, this is an easier thing to do, but is considered far more dangerous. Despite the popularity of angel magic however, it holds a few major flaws in reasoning. How one could compel a divine being into assisting with such an action is a mystery. Secondly, it hold the assumption that an angel could be compelled by man to do anything at all.