The verse is talking about the abheda (non-difference) that exists between yantra, mantra and devata.
There is a very similar verse in the Kularnava Tantra's 6th chapter (86th verse).
yantram mantramayam proktam devata mantrarupini | yantre sa
pujita devi sahasaiva prasidati ||
Yantra is endowed with mantras (or mantric qualities); and devata is
of the ...
king Vṛṣaṇaśva is mentioned in Rig-Veda mandala 1- Sukta 51-Mantra 13.Indra once took birth as a daughter of Vṛṣaṇaśva and her name was Mena.
As you requested , below are the three translations of the mantra where the king Vṛṣaṇaśva is mentioned in Rig-Veda.
Translation By H.H.Wilson
अददा अर्भां महते वचस्यवे कक्षीवते वृचयामिन्द्र सुन्वते | मेनाभवो