have been reading a long essay on psychology and, at some point, the authors use the phrase "in one's sum", whose meaning I could not catch. I looked it up at some dictionaries, but I could not find either the phrase or a possible meaning for it. The context is as follows:
“We seek to test and find ourselves in the intimacy of the therapeutic relationship, to become known to and accepted by the other, in whose sum we may more fully assess ourselves.”
"In their sum, we can then most fully assess our potential for life."
Can anyone help me understand this phrase? Thanks in advance.