p. 270
वेदानां चारपूर्वेण चैतद्विद्वन्ब्रवीमि ते ॥ ५१ ॥
In plain words
And this I tell you, knower — grounded in the Vedas, gone through first. || 51 ||
Close to the Sanskrit
And this, O knower, I speak to you by that which has the traversal of the Vedas as its antecedent. || 51 ||