I just hit Chp 4 "Magnesium and Calcium" in that book. Here are some select quotes:

Calcium and magnesium are opposites in their effects on our body structure. As a general rule, the more rigid and inflexible our body structure is, the less calcium and the more magnesium we need.

Both are required for optimum body function and health.

Calcium causes muscles to contract, while magnesium helps them relax.

Magnesium is essential for proper calcium absorption and is an important mineral in the bone matrix.