Why can't all cells preform all functions

You are correct all cells have the same coding; however they can only preform certain function.

So your question is why can a liver cell only be a liver cell despite the fact that they have all the genes as every other cell? When a liver cell is made, although it does have all the same genes as every other cell, not all of them are "turned on". So hypothetically if a cell has 26 genes labeled A-Z a liver cell may have genes A and B turned on while a cardiac cell has genes C and D turned on. All other that dont help a liver cell preform the function of a liver cell are turned off.

If ever cell was able to express every gene I feel all hell would break loose. For example in the small intestine you have S cells which secrete secretin into the blood which causes HCO3- to be released from the pancreas into the small intestine. You want HCO3- to be released into the small intestine because the stomach chyme is very very acidic and can cause harm to the intestines. So HCO3- (which is basic) is released in order to neutralize the chyme. If you had S cells in the stomach they would also cause the secretion of HCO3- in the stomach (which you obviously do not want since stomach chyme has to be acidic).

As we age our ability to create new cells that work properly decreases/ sometime we are just unable to do it in general. For example if you have a myocardial infraction (heart attack) a portion of your cardiac die due to lack of oxygen. You do not produce new cardiac cells there, when they are dead they are dead. This occurs because we have do not have stem cells which can go and make new cardiac cells when they die.

However scientist have discovered something that they are hoping to use in the future. They have determined that if you take you skin cells and turn three specific genes on then you can create a pluripoitent stem cell. These are not as good a embryonic stem cells, but they are still pretty good. So scientists believe that they may be able to do this in the future however they still have to complete many tests before it becomes main stream.

You asked: Why is the distinction of a "liver" being a liver necessary why cant it just be an organ that preforms many functions including those of kidneys/intestines/heart.
What makes a liver cell a liver cell is the genes which are turned on.

those are called specialist cells. they can't perform all functions because they don't have the parts that the other parts have.