The long and short of it is - they reduce the amount of enzymes your body takes to break the nuts down.  Raw nuts are full of enzyme inhibitors that slow down the digestive tract, which can lead to all sorts of issues (bloating, stomach cramps etc). If you soak the nut, the enzyme inhibitor is released and its nutrients are more easily absorbed. To activate your nuts, soak in water overnight and either dry them out in the sun or in the oven for 24 hours.