The undefiled law of the Lord is that love which bids men seek not their own, but every
man another’s wealth. It is called the law of the Lord as much because He lives in accordance with it as because no man has it except by gift from Him...
For what preserves the glorious and ineffable Unity of the blessed Trinity, except love? Charity, the law of the Lord, joins the Three Persons into the unity of the Godhead and unites the holy Trinity in the bond of peace...
It is the very substance of the Godhead...
Love is the eternal law whereby the universe was created and is ruled.
Saint Bernard of Clairvaux
On loving God,12
http://www.ccel.org/ccel/bernard/loving_god.i.html?highlight=st,bernard,of,clairvaux#highlight