Explain why energy should be conserved?

Not all energy sources will last forever. As you know, we can generate energy from many natural resources. Most often we mean gas, oil and coal. When burned, these substances release thermal energy, which is then used to meet the needs of mankind: for heating premises, as an open source of fire. But these resources will soon be exhausted. Deposits of natural combustible materials are not permanent. Humanity should gradually abandon these energy sources and completely switch to the energy of the sun, wind, water.