why the entropy is maximum at equilibrium stage???

Entropy of a system is defined as the degree of randomness of the system.The second law of thermodynamics states that entropy of a system always tends to maximum.A significant feature of all the spontaneous process is that they tend to reach an equilibrium stage.Like when ice melts the temperature of water formed increases untill it becomes similar to that of surroundings.Thus water and surroundings both reaches in the stage of thermal equilibrium.So as long as the spontaneous process in a system goes on,entropy goes on increasing untill it reaches a maximum value at equilibrium stage.That is at equilibrium deltaS = 0.Thus,the equilibrium in an isolated system is chatacterised by maximum entropy.