The Threefold Temporal Descriptions of God and Isaiah

Our series on the Old Testament in the book of Revelation opens with Rev 1:4a, where we find the phrase “who is and who was and who is to come, the Almighty.” The phrase is repeated in Rev 1:8 where parts of it are defined in an important way. Scholars are in general agreement that John gets the phrase from the Septuagint (LXX) Exod 3:14, but that verse accounts for only one-third of John’s wording. Where does the remainder come from? Why would John draw on Exod 3:14? What point was he trying to make?