What follows is my provisional translation (in other words, not official or authorized; see here for more) of a passage from a Tablet by ‘Abdu’l-Bahá, the original text of which has been published in Badáyi‘-i-Ma‘ání va Tafsír, p. 67. I recommend reading it in tandem with this passage from a Tablet of ‘Abdu’l-Bahá, in which He gives a historical interpretation of Dhu’l-Qarnayn, and this passage from another one of His Tablets in which He gives a figurative interpretation of that term.
As to the intended meaning of Dhu’l-Qarnayn [“the possessor of two horns”] in this verse,[1] it is none other than Muḥammad Himself—may the spirits of them that are nigh unto God be a sacrifice for Him—for He held the ranks of both Prophet and Guardian. We may alternatively interpret Dhu’l-Qarnayn as the Lord of East and West, for in His essence,[2] He was the One Who laid low the necks of all created things and wielded sovereignty over all existence on the part of God, the One, the Incomparable, the Almighty, the All-Wise.
In another sense, we may interpret the two horns as signifying steadfastness and virtuous character, inasmuch the people witnessed that none like unto Him [Muḥammad] had ever appeared on the earth, even as the Almighty addressed Him, saying: “And truly Thou art of an exalted character.”[3] God Himself doth suffice us, at this moment, as a Witness.
In yet another sense, we may interpret the two horns as the Qur’án and the Law, which God hath made a reminder and an admonition for those who have turned their faces unto Him, the Mighty, the Gracious. Verily, God assigned to Him [Muḥammad] a dwelling-place upon the earth and a seat of authority in this realm, and made Him a Sign of the Cause of all things, that He might establish the truth and eliminate falsehood, and cause the whole earth to be illumined with the light of the guidance of God, the Omnipotent, the Exalted, the Omniscient. For instance, God revealed unto Him the Qur’án to serve as a reminder for the people of insight, and the sword to be a lesson for the heedless.
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[1] Qur’án 18:83.
[2] Literally, “His primary reality” (al-ḥaqíqat al-awwalíyya).
[3] Qur’án 68:4.
A typescript of the original Arabic text of this passage appears below (all punctuation and vocalization mine).