Body has several impurities and develops many - in course of our actions and transactions - and even the lack of actions. Yoga exercises like soorya namaskaar -purify the body in a variety of ways - by removing all constrictions and rigidities at different places of the body and making it a one homogeneous unit. Body must feel - easy, healthy, light and as one homogeneous unit. If there are impurities anywhere, it feels uneasy, unhealthy, heavy, constricted and painful where the impurities are. But, these are easily removed by Yoga exercises like soorya namaskaar and aasanaas.
What are impurities of the senses and the mind? The ancient India knew well that "kaama,krodha,lobha,moha,mada,matsarya" are the six internal thieves or impurities that are robbing us of our mental purity and joy. Add to them the factor of fear. The list is complete. We must constantly beware of these internal enemies - and keep them off. When mind is devoid of them - it feels a rare joy - which really is its greatest treasure. The impurities are covering it - and obscuring it from our own self.
Purity of the body, mind and senses gives us hitherto unknown knowledge and powers on them. These powers are always there in the body, mind and senses. Just that - they were not available to us - because of the impurities surrounding them.
Remove the impurities - all these powers in them start shining. Eyes start seeing things which they never saw earlier. Ears hear sounds which they never heard earlier. Nose smells new smells. Skin feels new sensations. Tongue feels new tastes. Mind in all its purity starts exercising its vast powers of intuition. Body becomes lighter and a whole lot more enjoyable.
As you purify your mind, body and senses, you become much more happier and joyous.
In the first - you study your own self. In the very beginning of Yoga Sutras (v.1.3), Patanjali has emphasized that whoever witnesses simply, without pre-conditions and without judgments - realizes the self. Tadaa drashtuh svaroopevasthaanam.
Self-study happens by witnessing. There is no separate book for self study. You are the Book. All things you need to know are hidden in your own self. Self study is witnessing the self - without conditions, without pre-conceptions, without judgments. By such witnessing, self-study happens. There is no other STUDY involved - except witnessing.
As witnessing of self progresses, You will gradually move deeper and deeper into your own self - and know your deepest self. In the deepest self - is sitting your most loved being. You call it your ishtadevatha. Initially, it may have a name and form (like Rama, Krishna etc). As the self-study proceeds deeper and deeper, the names and forms will vanish but the ishtadevatha remains in our closest proximity.
At another level, Svaadhyaaya also can be initiated through study of the science (of yoga) or of scripture(like Sruthi, smrithi etc). These are great treatises on self-study.
We must remember that when we are witnessing the self or studying the self, the self gets centred and starts residing in the self (and does not wander outside of the self). Study of Srutis and the science of Yoga also leads us to the same result.
Whether you only realize your deepest self or come in communion with your most loved deity - the result finally is the same.