तस्मादृतुमत्यां महिष्यामृत्विजश्चरुमैन्द्राबार्हस्पत्यं निर्वपेयुः ॥ कZ_०१.१७.२४ ॥
tasmād ṛtumatyāṃ mahiṣyām ṛtvijaś carum aindrābārhaspatyaṃ nirvapeyuḥ
Therefore, when the chief queen is in season, the officiating priests should offer the Indra-and-Bṛhaspati oblation (aindra-bārhaspatya caru).
Because producing a legitimate heir is a core state-security objective; ritual also publicly reinforces legitimacy and elite consensus.