St. Dimitry of Rostov

First of all it must be understood that it is the duty of all
Christians – especially of those whose calling dedicates them to
the spiritual life – to strive always and in every way to be
united with God, their creator, lover, benefactor, and their
supreme good, by Whom and for Whom they were created. This is
because the center and the final purpose of the soul, which God
created, must be God Himself alone, and nothing else – God whom
Whom the soul has received its life and its nature, and for Whom
it must eternally live.