Isaiah 6:3

And one cried unto another (frequentat. impf.). Cf. Revelation 4:8.

Holy, holy, holy is Jehovah of Hosts:

That which fills the whole earth is His glory.

The word "holy," thrice repeated as if it struck the chord to which the whole nature of these pure beings vibrated (the ancient church found here an allusion to the mystery of the Trinity) sums up the meaning of the vision in so far as it is a revelation of God. The general notion of holiness is too complex to be analysed here. The root idea appears to be that of distanceor separation. As a predicate of deity it expresses first of all the awful contrast between the divine and the human, and then those positive attributes of God which constitute true divinity, and call for the religious emotions of awe, reverence and adoration. What Isaiah here receives, therefore, is a new and overpowering impression of the Supreme Godhead of Jehovah; the whole impact of the vision on his mind is concentrated in the word which he hears from the lips of the seraphim. Although the idea of holiness in the O.T. is never to be identified with that of moral purity, it is clear from Isaiah's immediate sense of guilt that ethical perfection is included among the attributes which make up the holiness or Godhead of Jehovah (see Robertson Smith, Prophets, pp. 224 ff.).

The second line of the Trisagion celebrates the "glory" of Jehovah, His manifestation of Himself in nature, one of the leading thoughts of the second part of this book (ch. 40 ff.). The seraphim contemplate the universal diffusion of this "glory" (sub specie aeternitatis) as a present fact; elsewhere it is an ideal yet to be realised: Numbers 14:21; Habakkuk 2:14.