Buddha-nature is great singleness of mind. Why? Because through singleness of mind the Bodhisattva-Mahasattva acquires all the perfections, from generosity to wisdom.
All sentient beings will without fail ultimately realize great singleness of mind. Therefore it is taught, “All sentient beings are possessed of Buddha-nature.” Great singleness of mind is none other than Buddha-nature. Buddha-nature is Tathagata.
—Shinran Shonin, Commentary on the Nirvana Sutra