Avatarika
क्रतुनिर्वर्तकस्याश्वस्य प्रजापतित्वमुक्तम्—'उषा वा अश्वस्य मेध्यस्य' इत्यादिना ।तस्यैवाश्वस्य मेध्यस्य प्रजापतिस्वरूपस्य अग्नेश्च यथोक्तस्य क्रतुफलात्मरूपतया समस्योपासनं विधातव्यमित्यारभ्यते ।पूर्वत्र क्रियापदस्य विधायकस्याश्रुतत्वात्, क्रियापदापेक्षत्वाच्च प्रकरणस्य, अयमर्थोऽवगम्यते ।
In plain words
The previous section identified the sacrificial horse with the cosmic creator, Prajāpati, beginning with the words, 'Dawn, indeed, is the head of the sacrificial horse.' Now, this next section begins in order to prescribe a unified meditation on that very horse (as Prajāpati) and the sacrificial fire, viewing them both as the ultimate fruit of the ritual. We know this is the intended meaning because no commanding verb was explicitly stated in the opening passage, and the context itself demands such a verb to complete its sense.
Close to the Sanskrit
The identity with Prajāpati of the horse that accomplishes the sacrifice has been stated by [the passage] beginning with 'Dawn, indeed, [is the head] of the sacrificial horse'. The collective meditation of that very sacrificial horse, whose nature is Prajāpati, and of the fire as described, as being of the nature of the fruit of the sacrifice, is to be prescribed—thus [this section] is begun. Because in the earlier part an enjoining verb was not heard, and because the context requires a verb, this meaning is understood.