The bilirubin in the bile isn't the part that aids in digestion. Bile is a mixture of quite a few things. Some of those things, like bilirubin, are wastes that the body is eliminating in the feces. Other components are functional.

One of the functional components of bile is bile salts. Bile salts are produced in the liver and they aid in digestion by emulsifying fats. Emulsification is important because it makes it easier for the enzymes that digest the fat (lipases from the pancreas, mainly) to access it.