Asana brings perfection and stillness in physical posture, asana will help to align your body geometry with cosmic geometry.
Pranayama brings perfection and stillness in breath, paranayama will help you connect yourself with supreme power and slowly you start getting supreme power like peace, purity, power, happiness, love, bliss and knowledge.
Paratyahara brings control on your ahar (आहार), we consume ahar like food, thought, feeling and other sensation coming to us using sense organ. Perfection of Paratyahar brings control in the senses, once that control is achieved you will not be driven by external situation. You will drive your life situations, which will help you to take control of your destiny. Once your destiny is in your hand then you can achieve whatever you want in life.
Yoga means moving forward step by step from Asana to paranayama and then to Paratyahar and further…
Yoga helps us to become master of our destiny.