The Lewis concept of describe the formation of bond in terms of sharing of one or more electron pairs and the octet rule. It does not explain the energetic of the bond formation and shapes of the polyatomic molecules.
The VB theory describes the bond formation in terms of hybridization and overlap of the orbitals. The overlap of orbitals along the intermolecular axis increases the electron-density between the two nuclei resulting in a decrease in the energy and formation of a bond.
