The figure depicts a nonpolar bond. Imagine the bond were polar and the bonding electrons being drawn in towards the more electronegative element. This would represent an additional electrostatic potential energy decrease in bond formation.
Polar bond formation represents an additional internal energy decrease. For this reason, polar bonds tend to be stronger than non polar bonds. This underlying concept is the basis for oxidation-reduction. The graphs of the electronegativities of the elements and their reduction potentials closely agree. Electronegative atoms pull electrons in closely when they form bonds, which is a favorable development from the point of view of energy.
This is the true inside story of redox. Oxidation-reduction gives a systematic way to account for this phenomenon by representing the chemical reaction process as a narrative of 'electron control' and standardizing the energy involved in tables of reduction potentials.
