Let us live in this love and this happiness, you and I and all of us, in the love of Christ and in contemplation, for this is where we find ourselves and one another as we truly are. It is only in this love that we at last become real. For it is here that we most truly share the life of One God in Three Persons.
God in His Trinity of subsistent relations infinitely transcends every shadow of selfishness. For the One God does not subsist apart and alone in His Nature. He subsists as Father and as Son and as Holy Spirit. These Three Persons are one, but apart from them God does not also subsist as One. He is not Three Persons, plus one nature therefore four! He is Three Persons but One God. He is at once infinite solitude (one nature) and perfect society (three persons). One infinite Love in three subsistent relations.
The One God Who exists only in Three Persons is a circle of relations in which His infinite reality, Love, is ever identical and ever renewed, always perfect and always total, always beginning and never ending, absolute, everlasting and full.
In the Father the infinite Love of God is always beginning and in the Son it is always full and in the Holy Spirit it is perfect and it is renewed and never ceases to rest in its everlasting source. But if you follow Love forward and backward from Person to Person, you can never track it to a stop, you can never corner it and hold it down and fix it to one of the Persons as if He could appropriate to Himself the fruit of the love of the others. For the One Love of the Three Persons is an infinitely rich giving of Itself which never ends and is never taken, but is always perfectly given, only received in order to be perfectly shared.
It is because the Love of God does not terminate in one self-sufficient self that is capable of halting and absorbing it, that the Life and Happiness of God are absolutely infinite and perfect and inexhaustible. Therefore in God there can be no selfishness, because the Three Selves of God are Three subsistent relations of selflessness, overflowing and super abounding in joy in the Gift of their One Life.
-Thomas Merton, New Seeds of Contemplation