I shall tell you the reason of this correctly as I have understood it. Both Nature and Individual Soul are without beginning and without end. Both of them are considered as supreme.
कारणं तु प्रवक्ष्यामि याथातथ्यं तु ज्ञानतः॥ अनादिनिधनावेतावुभावेवेश्वरौ मतौ।