The Riks or mantras of Rig Veda are not meant to destroy external enemies. The mantras composed and included in Tantra literature or some other black magic text may do that work.
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Consider Rig Veda 1.147.4
यो नो अग्ने अररिवाँ अघायुररातीवा मर्चयति द्वयेन । मन्त्रो गुरुः पुनरस्तु सो अस्मा अनु मृक्षीष्ट तन्वं दुरुक्तैः ॥
yo no agne ararivām̐ aghāyur arātīvā marcayati dvayena | mantro guruḥ
punar astu so asmā anu mṛkṣīṣṭa tanvaṃ duruktaiḥ ||
English translation:
O Agni, the ungenerous illusion (one) wishing us ill and full of hostility, who harms us by Illusion of separateness from BRAHMAN (his duplicity), let this mantra may be directed to break/destroy the illusion (he should bring harm upon his own body by his evil words).
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हेअग्ने नोऽस्मान् युष्मद्रक्षितान्यःअघायुः मारणादिरूपपापेच्छावान् अररिः अदाता अस्मद्दानप्र- तिबन्धकइत्यर्थः रातेश्छान्दसस्यलिटःक्वसुः अरातीवास्वयमदानवान् छन्दसिवनिप् तदिच्छतीतिम- त्वर्थीयोवनिप् शत्रुत्वमाचरन्यः शत्रुः द्वयेनमानसवाचिकभेदेन द्विविधेन नददामी तिमानसोमन्त्रः निन्दाद्यारोपेणदाननिवारणंवाचिकोमन्त्रः यद्वा मायाहेतुकेन विरुद्धरूपेणद्विविधेनमन्त्रेणयोविरुद्ध- माचरति तन्नसंकीर्तयति यच्चप्रियंब्रूतेतन्नकरोति अन्यद्वदतीत्येवंमंत्रस्वरूपद्वेबिध्यम् पूर्वंमानसवा- चिकभेदेन इदानींवाचिककायिकभेदेनेतिविवेकः ईदृशेनमन्त्रेणयः शत्रुर्मर्चयति भर्त्सयति विधेयीक- रोतिवास्मान्समंत्रैकदेशेमानसरूपः अस्मैपुनर्गुरुरस्तु षष्ठ्यर्थे चतुर्थी प्रयोक्तुरेवपुनर्गरितास्तु तथा- दुरुक्तैर्दुर्वाक्यैः निन्दारूपैर्वाचिकैः तन्वं स्वकीयां तनुंअनुमृक्षीष्ट अनुमार्ष्टु अनुक्रमेणलुंपतु यद्वा सद्वि- विधोमन्त्रः अस्मैप्रयोक्तुरेवगुरुर्गरितास्तु अन्यान्यप्यस्मन्न्यक्वारायप्रयुक्तानिनिष्ठुरभाषणानिसन्ति तैर्दुरुक्तैः सोरातिः तनुमेवावलुंपतु स्वात्मानमेवावृत्यदहत्वित्यर्थः ॥
English Translation
"O Agni! May any sinful, murderous enemy who wishes us harm—one who is non-giving (miserly), meaning he creates obstacles to our acts of giving—or one who acts with hostility out of his own lack of generosity, may he be subdued.
The enemy acts with hostility through a two-fold method: mental and vocal. The 'mental' method involves the inner thought of 'I will not give.' The 'vocal' method involves preventing others from giving by throwing insults and blame.
Alternatively, the dual nature of his trickery can be seen when he speaks pleasantly but acts contrary to his words, or says one thing and does another. The previous distinction was between mental and vocal; this distinction is between vocal and physical.
Whoever is such an enemy that threatens us or seeks to control us with this two-fold manipulation, may that very manipulation turn back heavily upon him (the instigator) instead. Furthermore, with his own harsh, insulting, and wicked words, may he destroy his own body (self-destruct).
In other words, may that dual-fold manipulation prove dangerous to the one who employs it. Whatever other harsh words he uses to humiliate us, may that hostile enemy ruin his own physical form with those very insults. The ultimate meaning is: let him envelope and burn his own self."
The phrase "marcayati dvayena" in the Rik does not indicate any physical person with evil in thoughts and speech and the mantra does not harm any physical enemy's body - as Sayana averred, but indicates esoterically the status of being engulfed in the illusion of separateness from the all-pervading BRAHMAN/pure consciousness - Dvaita, thus, harming the individual only from not getting rid of illusion of separateness.
The utterance of mantra, consequently, will destroy the illusion of duality or DITI, and the formless ENERGY or ADITI is experienced.
