The word svadhyaya contains an ambiguity its interpreters have used deliberately. Read one way it is sva-adhyaya, one's own study, the personal recitation of scripture; read another way it is study of the sva, of the self. Classical usage supports the first reading, and the Vedic institution of daily recitation is plainly what the older texts mean. But the second reading was too apt to leave alone, and later teachers, especially in Vedanta and in the modern transmission of yoga, promoted it from pun to doctrine. On this account the practitioner engages scripture not to store it but to be shown to themselves by it: the text is a polished surface, and what one meets in sustained study is one's own mind, its evasions, its favorite consolations, the passages it flinches from.
Mantra repetition, which Patanjali's commentators include under svadhyaya, works the same way; a syllable repeated ten thousand times becomes a background against which the mind's motion is visible as it never is in silence. The two readings converge in practice. Recitation without self-observation degrades into mechanical piety; introspection without a text degrades into rumination, the self examining itself with its own crooked instruments. Svadhyaya, held whole, is the discipline of placing one's mind against something older, harder and better than itself, regularly enough that the differences become instructive, and the fruit Patanjali names, communion with one's deity, describes where that discipline arrives.