Bhashya
अतीतविद्याप्राप्त्युपसर्गशमनार्थी शान्ति पठति—श नो मित्र इत्यादि ।व्याख्यातमेतत्पूर्वम् ॥
In plain words
The text recites the peace invocation beginning with 'May Mitra be good to us' in order to dispel obstacles concerning knowledge already studied. This has already been explained.
Close to the Sanskrit
The text recites the peace invocation beginning with 'May Mitra be auspicious to us' for the purpose of subduing obstacles to the attainment of past knowledge. This has been explained previously.