14Thus said the Lord,
Your Redeemer, the Holy One of Israel:
For your sake I send to Babylon;
I will bring down all [her] bars,
And the Chaldeans shall raise their voice in lamentation.
15I am your Holy One, the Lord,
Your King, the Creator of Israel.
16Thus said the Lord,
Who made a road through the sea
And a path through mighty waters,
17Who destroyed chariots and horses,
And all the mighty host—
They lay down to rise no more,
They were extinguished, quenched like a wick:
18Do not recall what happened of old,
Or ponder what happened of yore!
19I am about to do something new;
Even now it shall come to pass,
Suddenly you shall perceive it:
I will make a road through the wilderness
And rivers in the desert.
20The wild beasts shall honor Me,
Jackals and ostriches,
For I provide water in the wilderness,
Rivers in the desert,
To give drink to My chosen people,
21The people I formed for Myself
That they might declare my praise.
22But you have not worshiped Me, O Jacob,
That you should be weary of Me, O Israel.
23You have not brought Me your sheep for burnt offerings,
Nor honored Me with your sacrifices.
I have not burdened you with meal offerings,
Nor wearied you about frankincense.
24You have not bought Me fragrant reed with money,
Nor sated Me with the fat of your sacrifices.
Instead, you have burdened Me with your sins,
You have wearied Me with your iniquities.
25It is I, I who—for My own sake—
Wipe your transgressions away
And remember your sins no more.
26Help me remember!
Let us join in argument,
Tell your version,
That you may be vindicated.
27Your earliest ancestor sinned,
And your spokesmen transgressed against Me.
28So I profaned the holy princes;
I abandoned Jacob to proscription
And Israel to mockery. Isaiah 43/14hb-28 Tanakh JPS 1985.
16Then Isaiah said to Hezekiah, “Hear the word of the Lord: 17A time is coming when everything in your palace which your ancestors have stored up to this day will be carried off to Babylon; nothing will remain behind, said the Lord. 18And some of your sons, your own issue, whom you will have fathered, will be taken to serve as eunuchs in the palace of the king of Babylon.” 2 Kings Chapter 20/16-18 Tanakh JPS 1985
The prophet Isaiah’s name, meaning “God is salvation,” serves as the title of the book. Isaiah son of Amoz is called to prophesy in the year that King Uzziah dies (ca. 740 b.c.e. and continues his work at least until 701 b.c.e Of his personal history we know little. His wife, “the prophetess,” and his sons, whose names bear witness to his prophetic announcements, are mentioned. He has access to the kings of his time (Uzziah, Jotham, Ahaz, and Hezekiah).
Summary of the Book of Isaiah at taggedtanakh.org (excerpt).
Ezra consists of two sections, with a considerable interval of time between the writing of the two. The first is an account of the return of the Jews from Babylon at the beginning of the reign of Cyrus, 538 b.c.e., and of the rebuilding of the Temple. The second, which takes place more than half a century later, tells of the second return of exiles in the seventh year of Artaxerxes (457 B.C.E.), led by Ezra. The entire period covered by the book extends over 79 years.
Summary of the Book of Ezra at taggedtanakh.org (excerpt).
Isaiah lived in the time of King Hezekiah who reigned over Judah in Jerusalem from 726-697 b.c.e. ninety years before the exile of Judah to Babylon in 587 b.c.e.
The Babylon exile lasted for seventy years before the defeat of the Assyrians by Cyrus the Great of Persia. The Assyrians had defeated the Chaldeans and Babylonians before Cyrus became G-d’s anointed King (Moshiach). Later Cyrus issued a declaration that the people of Israel could return to Jerusalem and rebuild the Temple.
In Isaiah 43/28 G-d says “I abandoned Jacob to proscription And Israel to mockery”. This is the complete exile of all the people Israel to Assyria with the deportation of Judah to Babylon being last. The exile of the northern kingdom and tribes across the river Jordan to Assyria having occurred many years earlier.
In Isaiah 43/19 G-d says “I am about to do something new (“a new thing” Tanakh JPS 1917); Even now it shall come to pass, Suddenly you shall perceive it: I will make a road through the wilderness And rivers in the desert.”
The road is cleared by the declaration of Cyrus of Persia for all of Israel to return and build the second Temple. And that was the sign that the Jewish people were forgiven of all their sins.
The book of Ezra tells the story of the return of the exiles from Babylon and another return some fifty years later from Persia.
There is no mention in the Tanakh of the Jewish people who built the second Temple knowing of the forgiveness of their sins declared by G-d in the book of Isaiah long before the exile of Judah began.
Whether the Jewish people knew of the forgiveness of their sins is unknown. How it was interpreted by the religious leaders if they were aware of it is unknown. We do know from the book of Ezra and Nehemiah that sinning was still an issue with the religious leaders after the Temple was built.
The new covenant of sin forgiveness for a time to come declared by G-d in Jeremiah (31/34) is delivered by messenger with the angel of the covenant according to the book of Malachi. And the messenger is Elijah.
The book of Malachi does not specify who the messenger is to deliver the message to or whether it is important that the Jewish people are aware that the time to come has arrived.
That will be up to the religious leaders of the Jewish people who have to believe that Elijah is who he says he is and the message he delivers.
I, for one, would want to know.