I saw the LORD sitting on a throne, high and exalted, and the train of his robe filled the temple (Isa. 6:1).
Isaiah sees a vision of YHWH. Seated on the throne of supreme majesty, he is the most extraordinary being in the universe. The prophet is overwhelmed by his splendor and glory. However, he is also struck by his purity. God’s perfection causes Isaiah to suddenly be aware of his own imperfections. The God of the universe seems unapproachable:
Then I said, “Woe is me! I am doomed! It is because I am a man of unclean lips … and I have seen the King, the LORD of hosts” (Isa. 6:5).
Later in Isaiah we find another prophecy about God. In contrast to the earlier vision, the prophet exclaims:
For surely you are our Father, though Abraham does not know us and Israel does not acknowledge us. You, O LORD, are our Father; Our Redeemer from of old is your name (Isa. 63:16).
It is the same God in both cases. However, we now see that the God of the universe is the Father of his people. He is indeed approachable. He is capable of “compassion” (v. 15). And this one who is their Father is the only one who is God:
From days of old, no one has heard, no ear perceived, nor has any eye seen a God besides you, who works on behalf of those who wait for him. But now, O LORD, you are our Father. We are the clay, you are the potter; all of us are the work of your hand (Isa. 64:4, 8).
If we were to see God, we would likely react as Isaiah did. We too would be overwhelmed by his glory and majesty. Standing before him, we might find ourselves suddenly aware of our failings and weaknesses. But we would also see that he is a God of “tenderness” and “compassion.” He is not distant and uncaring. He is approachable; the Father of his people. And in the presence of such greatness, we would know with absolute certainty that he alone is God. It is impossible that there would be another like him:
With all that I am I will exclaim, “Who is like you, LORD? You deliver the weak from those too strong for them, the poor and needy from those who rob them” (Ps. 35:10).
He sits in the heavens but has concern for the troubles of human beings. In him we find not only someone greater than ourselves, but someone better than ourselves. He is the only one worthy to be called the God of the universe. His goodness is complete. God by his nature defines goodness.
This God is not only supreme in power but also in virtue. He is incomparable in qualities and character and he desires that people would be like him. He is our Father. But to truly be his people, we must love the things that he loves. We must love our fellow human beings.
This God won the hearts of his people. The people of the nations sometimes serve their gods from stark fear and vulgar desires. In the Bible, we find people who serve their God because of his qualities. They admire him. They esteem him. His goodness is beyond measure. Who is like YHWH? No One!
Gill, J. Dan (2016). He is Their Father. In, The One: In Defense of God (pp. 45-47). Nashville, TN: 21st Century Reformation Publishing.
 The use of “holy, holy, holy” in addressing God (v. 3) is an emphatic which intensifies the declaration of God’s purity and separation from all other beings. There is of course no indication of a Trinity here, as only the Father is being viewed and addressed.
 It may rightly be said that God himself is the only one who is intrinsically good. He is good in a sense in which no one else can be compared (1 Sam. 2:2). On this point notice also the teaching of Jesus in Mark 10:18 and Luke 18:19.
 God is kind toward the weak and resists their oppressors. He teaches that his people must be of that same heart (Ps. 82:3, 4; Jer. 22:3).