G-d commanded Moses and Aaron to tell the people to offer up the Passover sacrifice annually on 14 Nissan.
Do not eat any of it half-cooked or cooked in water, but only roasted over the fire, together with its head, its legs, and its internal organs.
Exodus 12:9
Allegorically, the “head,” “legs,” and “internal organs” of the Passover offering signify the three dimensions of spiritual life.
The “head” is the study of the Torah; the “legs,” i.e. the limbs of action, are the active performance of the commandments; and the “internal organs” refer to prayer, the inner life of the soul.
All three must be totally permeated by the “fire” of holiness -- the warmth and enthusiasm for G-d.
-- Daily Wisdom Volume 3