There are a couple of interesting things to point out from today's Old Testament passage. The first thing that struck me in consulting the Fathers is the unanimity with which they find the Trinity referenced and worshiped in the angelic cry, "Holy, holy, holy is the LORD of Armies/Hosts!" Fulgentius is representative of the early church's understanding and writes, "The prophet Isaiah did not keep silent about this Trinity of persons and unity of nature revealed to him, when he says he saw the seraphim crying out, 'Holy, holy, holy, Lord God of hosts.' Therefore, where the triple 'holy' is repeated, there is the Trinity of persons; where 'God Lord of hosts' is said but once, we recognize the unity of the divine nature. Therefore, in that Holy Trinity—and I keep on saying it so that it may be fixed in your heart the more firmly—the Father is one, who alone by his nature has generated the one Son from himself; and the Son is one, who alone has been born from the nature of the one Father; and the Holy Spirit is one, who alone proceeds from the essence of the Father and the Son" (Fulgentius of Ruspe, To Peter on the Faith). This is another interpretation that would have made my Old Testament professors cringe insofar as this understanding is clearly one of reading Isaiah through the lens of Christ instead of first letting the text stand on its own, but as I've said before, given the agreement from such theological giants in the early church such as Theodoret, Cyril, and Jerome, perhaps it is our 'enlightened' and 'sophisticated' hermeneutic that needs humble correction instead of suggesting that those much closer to Christ and the Apostles were consistently mistaken in their understanding of Scripture.
A more familiar portion of today's lesson is Isaiah's response to being in the presence of God. "Woe to me for I am ruined because I am a man of unclean lips and live among a people of unclean lips, and because my eyes have seen the King, the LORD of Armies" (Isaiah 6.5 CSB). Though we certainly give lip service to the holiness of God, the casualness and nonchalance with which we in Protestantism tend to approach worship betrays our confession. While we may and must approach God as a loving Father, he is at the same time completely holy and perfectly righteous--which we are definitely not. As such, worship without awe and reverence is misguided at best. Let us not approach worship with fear of judgment but with a holy reverence and awe-filled appreciation for the incredible blessing it is to approach the God of the universe through the righteous covering of Christ. "Let our lips be touched by the divine coal, which burns away out sins and consumes the filth of our transgressions" (Cyril of Alexandria, Commentary on Isaiah).