The Hidden Ground of Love by Thomas Merton, published in 1985, is a collection of his letters that included religious or spiritual experience as well as social concerns.
In the Introduction, William H. Shannon, General Editor of the Merton Letters, quotes Merton:
And the deepest level of communication is not communication, but communion. It is wordless. It is beyond speech, and it is beyond concept. Not that we discover a new unity. We discover an older unity. My dear brothers (and sisters), we are already one. But we imagine that we are not. And what we have to discover is our original unity. What we have to be is what we are.
Earlier in the Introduction, Shannon quotes Merton writing of
…the happiness of being one with everything in that hidden ground of love for which there can be no explanation.
William Shannon adds
These words which see God not as a being among other beings but as the ground of all beings, and even more precisely the, ground of love in which all beings find their identity and uniqueness, provide a most appropriate title for this volume.