Svadhyaya. Sva means self and adhyaya means study or education. Education is the drawing out of the best that is within a person. Savadhyaya, therefore, is the education of the self.
Svadhyaya is different from mere instruction like attending a lecture where the lecturer parades his own learning before the ignorance of his audience. When people meet for svadhyaya, the speaker and listener are of one mind and have mutual love and respect. There is no sermonizing and one hear speaks to another. The ennobling thoughts that arise from svadhyaya are, so to speak, taken into one's bloodstream so that they become a part of one's life and being.
The person practicing svadhyaya reads his own book of life, at the same time that he writes and revises it. There is a change in his outlook on life. He starts to realize that all creation is meant for bhakti (adoration) rather than bhoga (enjoyment), that all creation is divine, that there is divinity within himself and that the energy which moves him is the same that moves the entire universe.
Philology is not a language but the science of languages, the study of which will enable the student to learn his own language better. Similarly, Yoga is not a religion by itself. It is the science of religions, the study of which will enable a sadhaka the better to appreciate his own faith.
Here's a video from MC Yogi: