Yoga encompasses not just the postures (asana) but also 7 other components (including pranayama and meditation) making up the 8 limbs of yoga. I'll only cover here the postures or the physical element. With regular practice, depending on the type of yoga, asanas can build strength, stamina, flexibility, focus and balance.
Synchronizing breath with movement together with mindfulness on all body sensations, the practice can bring about a speedy transformation to the individual.
Yoga goes beyond fitness. It acts as a hub for everything in your life. It pulls together your career, love life, family, social life, etc. into a seamless singularity. You don't feel scattered all over the place. Imagine a sardine bowl - millions of individual sardines that move in unison, as though they are being held together by a single intelligence.
A great mystery of yoga for me is how you continue your evolution as a human being. Imagine. Here you are, holding a pose, synchronizing breath with movement in full mindfulness...and you develop compassion! You become a better human being, respectful of life and mindful of how your actions and thoughts ripple through this universal fabric that affects all of us. Yes, you get to tap into the interconnectedness of everything. Perhaps you even rediscover and redefine divinity as life unravels. Pose + breath + mindfulness + intention can do all that? That's yoga's mystery.