Translation: Once again, the KJV is not sufficiently clear on the intent of this passage. In Gileadi's translation:
"Look to Abraham, your father,
to Sarah, who bore you
He was but one when I called him,
but I blessed him by making him many." (P. 197)
In Today's English Version of the Bible, the text reads:
"Think of your ancestor, Abraham, and of Sarah, from whom you are descended. When I called Abraham, he was childless, but I blessed him and gave him children; I made his descendants numerous."
These two agree in theme, and that theme is not absent in the KJV, only buried. The text is pointing out Abraham and Sarah and the foundation of the lineage, and reminding Israel of God's relationship and covenant with Abraham.
Scriptural analysis: Isaiah sends the followers of righteousness back to Abraham and Sarah. By reminding them of their forefathers, he also reminds them of the covenant that he made with Abraham. Abraham's blessing was to be a father of nations, and in this verse that reminder is made explicit. In addition to the people, Israel is being told to look to the Abrahamic covenant.
Meaning for Jacob's audience: This message is clearly for the literal descendants of Abraham in his audience. It is a reminder to them of their heritage and covenant status.