The THC in order for it to be able to be fully absorbed through the stomach lining needs to be converted to THCA. This occurs when the THC reaches a certain temp. The second reason is the when you heat the oil and THC it allows the THC to break down and mix with the oil. As far as BCBUDDY's comment I agree. Oil has a tendency to go rancid quickly with organic matter. keep you oil in an airtight sealed container in the fridgerator when not in use. Hash or Keif make great substitues to using marijuana bud of leaf because, you are not putting clorphyll in your product. (spelling is atrocious, just woke up)