Kabbalah sa Exodo 11:4: Sha'arei Orah

Now, when our teacher Moshe, peace be upon him, came to inform Pharaoh of the plague of the death of the firstborn, he hinted that it would be actualized through the Divine quality of Koh-כה. He therefore stated,²³⁷Exodus 11:4-5 “Thus-Koh-כה said HaShem-יהו״ה, ‘At about midnight I shall go out in the midst of Egypt. Every firstborn in the land of Egypt shall die etc.’” It is about this that our sages, of blessed memory, stated,²³⁸Liturgy of Passover Haggadah; Sifri Devarim 301:18; Yalkut Shimoni Exodus 12; Ramban to Exodus 12:12 and elsewhere. “I shall go out in the midst of Egypt – I-Anee-אני, and not and angel; and I shall strike every firstborn – I-Anee-אני, and not a Seraph, etc.”