Is.6:1-13-The year would be around 740 with Assyria on the move.
1) We sing Holy, holy, holy. It is repeated in Rev.  What do we mean by holy. I almost never here the word, except for holier than thou or Holy Land. Rudolph Otto is the classic work on holiness, still.

2) Seraphs=fiery or shining ones; one would assume winged serpents, perhaps. Serpent symbolism is a deep subject, see a religion encyclopedia or for instance, Karen Jones.

3)Notice that this is a temple vision that touches heaven. this makes sense as they saw the temple as a sort of connection point, a nexus, between heaven and earth. The symbolic ark throne becomes a heavenly one. Again, John's vision is a worship vision.

4)Notice that we have resistance, again, to a call. This time a deep lament. One detects a sense that to see God was more than mortals can bear.

5) An angel cleanses the lips as opposed to God touching the lips of Jeremiah from last week's reading.

6) Here I am is almost the proper standard response.

7) I see Glory as the manifest presence of God. God seems to be speaking to the divine council.

8) The prophecy itself, 9-10, is used in the gospels. It appears to me that the people won't or can't hear properly until they are brought low, to reach the bottom of the well.