What makes metabolism possible?

There is one simple answer to this and then a very very long and complicated one that explains the simple one. Metabolism is a necessary result of the vast number of chemical reactions releasing energy every second of every day in each person's body in order to keep them alive in a biological sense of the word. This is one of the most complex and intense scientific areas of study on the planet and you can get very deep into complicated chemical equations, but the bottom line is this: organism's die without a continuous supply of fuel. Similar to putting gas in your car, the only difference is your car doesn't die it just stops running if you don't put gas in it. People die and don't come back by shoving more food down a dead body's throat.