Rules of moral self-control in conduct .Yama is, more largely, any self-discipline by which the rajasic egoism and its passions and desires in the human being are conquered and quieted into perfect cessation. The object is to create a moral calm, a void of the passions, and so prepare for the death of egoism in the rajasic human being. 
A plunge into all the profundities of the soul. Union with the Divine - a union either transcendental (above the universe) or cosmic (universal) or individual or, as in our yoga, all three together. 
Yoga is in essence the union of the soul with the immortal being and consciousness and delight of the Divine effected through the human nature with a result of development into the divine nature of being, whatever that may be, so far as we can conceive it in mind and realise it in spiritual activity. 
All yoga is in its nature an attempt and an arriving at unity with the Supreme. 
It is the supreme Godhead who manifests both containing self and its contained phenomena by the power of his spiritual consciousness. 
For the Purushottama within is not readily manifest to any and every being; he conceals himself in a thick cloud of darkness or a bright cloud of light, utterly he envelops and wraps himself in his Yogamaya. 
Yogi and Sadhaka
The Yogi is one who is already established in realisation—the sadhak is one who is getting or still trying to get realisation.
A sadhaka is one who is doing sadhana to attain union with the divine consciousness. A Yogi is one who is already living in some kind of oneness with the Divine, not in the ordinary consciousness.