In this passage, St. Teresa famously describes the Seventh Mansion, Union, as “water in water.”
“…here it is like rain falling from the heavens into a river or a spring; there is nothing but water there and it is impossible to divide or separate the water belonging to the river from that which fell from the heavens. Or it is as if a tiny streamlet enters the sea, from which it will find no way of separating itself, or as if in a room there were two large windows through which the light streamed in: it enters in different places but all becomes one.”