Difference.

It is said that 'multiplicity in unity is the law of the universe' (Abiel Abbot Livermore, The Epistles of Paul to the Corinthians, Galatians, Ephesians, Philippians, Colossians, Thessalonians, Timothy, Titus and Philemon, 1881, p. 59). I posit that the purpose of the universe is love, which is why there is difference.
~ Wald Wassermann