How are prescription tablets/capsules absorbed into a body?

I have been diagnosed with celiac disease. Apparently, the villi grab the nutrients from food in the small intestine, but with C/D, this doesn't happen. I guess my first question would be, "Why take vitamin/nutrient supplements" if the villi aren't going to "grab" them. Likewise, why take any prescription medication, if they will not be absorbed into the body? Of course, that would only pertain to oral tablets/capsules.