In parashat Vayikra (3:9)the kidneys are referred to as "העצה". Rashi comments explains that they are called this because they give advice. In what way to kidneys give advice?
My rav gave a drasha during Yom Kippur related to the expression בוחן כליות which means, literally "checks the kidneys".
The adrenal glands are located on top of each kidney. Adrenaline is one of several hormones that increase or decrease excitement. The metaphor of בוחן כליות is that G-d is checking how excited you are in performing mitzvot.
Other than excitement, the renal glands are mainly responsible for homeostasis, which, in a sense is an "advisory" function. Hormones are secreted only when necessary, and in a sense, they "advise" other parts of the body how to "behave" or react.
As an example, when there is danger, the renal glands (kidneys) secrete the adrenaline that allows the "fight of flight" response, which speeds your blood pressure / heart rate and, most importantly, "advises" your brain how to react to the danger (flee or defend yourself).
In short, without the renal glands and this "advice". you couldn't function well, if at all.