You ask, "What is an ellipsis? I have learned about chiasms, what is an ellipsis?" According to E. W. Bullinger, ellipsis appears in the Bible when "a word or words are omitted … in order that we may not stop to think of, or lay stress on, the word omitted, but may dwell on the other words which are thus emphasized by the omission."
When the ellipsis appears within a literary structure such as a chiasm, it behaves as if it were there. This literary device is best seen by illustration. Below is John 16:16-19. The phrase
A little while, and you will no longer see Me; and again a little while, and you will see Me.
appears three times. The fourth time, the one with the ellipsis, is shown in violet. The ellipsis makes it appear that the entire phrase was stated even though it was omitted.
A | “A little while, and you will no longer see Me; and again a little while, and you will see Me.” (v16) | ||
B | Some of His disciples then said to one another, “What is this thing He is telling us, ‘A little while, and you will not see Me; and again a little while, and you will see Me’ (v17A) | ||
X | and, ‘because I go to the Father’?“ (v17B) | ||
B′ | So they were saying, “What is this that He says, ‘A little while’? We do not know what He is talking about.” (v18) | ||
A′ | Jesus knew that they wished to question Him, and He said to them, “Are you deliberating together about this, that I said, ‘A little while, and you will not see Me, and again a little while, and you will see Me’?” (v19) |
Once I learned from Bullinger how to recognize the ellipsis, my understanding of chiastic and other structures became even more clear. I hope it helps your analysis, too.