Yoga is a tradition that has always embraced the idea of working with prana (life force energy) to move toward more power and ease. Whether the practitioner wanted to empower, heal, vitalize or calm herself, yoga offered specific methodologies for moving her in the direction of her needs.
The navel was always a central focal point for working with energy, due to its transformational and balancing capacities. Tantra understands that bringing more focused, loving attention to this area can ignite the positive qualities associated with a belly that is alive.
In fact, the yogis spent considerable time and effort in strengthening this flame, using a variety of different techniques. Chances are that if if you have taken a yoga class, you yourself have worked to stoke the fire of the core. Every time you consciously breathe out and feel the navel draw back on the spine, you stoke the navel flame. When you draw the navel lock upward for Uddiyana Bandha, this flame is sparked. When you do a strong breath practice such as Kapalabhakti or Bhastrika, the light of the belly is brightened. It can also be subtle, such as the simple awareness of the way your belly drops down on your spine effortlessly as you melt into a deep restorative backbend or in Savasana.
Why so much focus on the belly? Well, when you have strong prana in your core, you can burn through anything life throws your way. When your prana flows intelligently at this navel center, you get better at digesting things, whether it be the salad you ate for lunch, the incredibly long report you need to read for work, or the less-than-desirable aspects of your personality that lead you away from freedom and joy.
Tantriks likened this part of our energetic anatomy to a fire because an alive belly warms us. It makes us feel safe and "at home" in our body. The belly, when full of presence, strengthens our sense of individual purpose in the world. A belly that is awakened says, "I am safe. I am here. I have a mission." A belly that is asleep says, "What's my unique purpose? Am I important? Am I balanced?"
The navel is also the seat of digestion and assimilation. If the navel (and sacrum in general) is weak, we may experience instability in our low back, sluggish digestion, or instability in our mind and emotions. I have found Forrest Yoga and ParaYoga to be two styles that pay particular homage to the belly fire, both on a physical and psychic level. Try taking one of these classes for a core-building and purifying experience.
You can also just practice bringing more loving focus to this area during your yoga practice, and during your daily life. With more kind presence at this area, you can begin to unearth your hidden capacities to be stable and solid in the face of a turbulent life.