Bhashya
एष ह वै यजमान एववित् यथोक्तस्य सामादेर्विद्वान्यज्ञस्य मात्रा यज्ञयाथात्म्य वेद यथोक्तम् ।य एव वेदेतिद्विरुक्तिरध्यायपरिसमाप्त्यर्था ॥
In plain words
This person is truly the knower of the sacrifice. Understanding the sāman and other elements as described, he knows the true nature and measure of the sacrifice. The repetition of 'whoever thus knows' marks the conclusion of the chapter.
Close to the Sanskrit
This indeed is the sacrificer who knows thus; knowing the aforementioned sāman and other elements, he knows the measure and true nature of the sacrifice as stated. The repetition 'whoever thus knows' is for the purpose of concluding the chapter.