First off you have to understand that comparing these two is like comparing oranges to lemons. They are both citrus fruits, but have completely different properties. Where Hemp and Marijuana are both part of the cannabis family, but both have different properties and different uses.
Marijuana is high in THC, but very low in CBD. This plant is grown with the intentions of using THC as a naturalistic way of aiding with certain ailments. This plant is also grown specifically to produce a lower amount of seeds and a higher amount of flower.
Hemp on the other hand is high in CBD but very low in THC levels. All parts of the Hemp plant are used for multiple ailments, topical applications, etc. Hemp is grown specifically to produce a lot of seed and very little flower.
Just based on the way these two plants are grown shows the significant difference in the two plants. Marijuana CBD will naturally have a higher THC content, which can cause psychoactive properties. Where Hemp CBD contains .3 of 1% THC which is in no means enough THC to get any psychoactive effects. .