The Nernst equation is essential for calculating the electrode potential of an electrochemical cell under non-standard conditions. It relates the cell potential to the standard electrode potential, temperature, and the concentrations of the reactants and products involved in the electrochemical reaction. By using the Nernst equation, one can determine how changes in concentration affect the voltage, thereby predicting the behavior of the electrochemical system under varying conditions. This is crucial for applications in batteries, fuel cells, and corrosion studies.