This dissertation interprets a body of textual material from the earliest stratum of Chinese formulations of "buddha-nature" thinking. Buddha-nature discourse is widely acknowledged as one of the key themes in the doctrinal aspect of Chinese Buddhism from the earliest times up to the modern debates around "Critical Buddhism." Scholarship has focused mainly on its later manifestations (esp. the Dasheng qixin lun and after), leaving its beginnings relatively understudied. In this thesis, I go back to these beginnings, and trace some early, arguably the earliest, evidence for this phenomenon to the surviving writings of the early fifth century exegete Sengrui. I position this evidence in the broader cultural context of late fourth--early fifth century Chinese Buddhism's changing conceptions of scriptural authority. I argue specifically that in this body of primary material, "buddha-nature" serves as a metaphysical warrant for an ideal of universal canonicity: a nonconceptual luminosity of mind that validates the textual, hence quintessentially conceptual, totality of scripture, in an historical moment when Buddhism in China for the first time must define itself as a coherent religious entity.