The sages connected Israel's acceptance of the Covenant at Sinai (kol asher diber Adonai na'aseh) with the response of the Prophet Isaiah (יְשַׁעְיָהוּ הַנָּבִיא) to the LORD's question, "Whom shall I send, and who will go for us?" Isaiah's answer, "Here am I" (הִנְנִי) was the same word used by both Moses and Samuel when they had encountered the LORD.
God then commissioned Isaiah to go tell the people, listen again and again (but do not understand); look again and again (but do not see). As with Pharaoh, the heart of the listeners would be hardened and the message would be disregarded. When Isaiah asked how long he should preach, the LORD said until their cities are all destroyed and their people are exiled from the land. Nevertheless, a "holy seed" (זֶרַע קדֶשׁ) would remain from which the people would one day be regenerated.
קָדוֹשׁ קָדוֹשׁ קָדוֹשׁ יהוה צְבָאוֹת
מְלא כָל־הָאָרֶץ כְּבוֹדוֹ
ka·dosh ka·dosh ka·dosh, Adonai Tze·va·ot,
me·lo khol ha·a·retz ke·vo·do
"Holy, holy, holy is the LORD of hosts;
the whole earth is full of his glory!"
Hebrew Study Card
One of Isaiah's first jobs was apparently to reassure King Ahaz (אָחָז) of Judah that despite the threat of invasion by the Northern Kingdom (i.e., Israel) allied with Syria, God would intervene and not allow the invasion to succeed. Moreover, a coming king was promised to Judah who would restore righteousness forevermore:
כִּי־יֶלֶד יֻלַּד־לָנוּ בֵּן נִתַּן־לָנוּ וַתְּהִי הַמִּשְׂרָה עַל־שִׁכְמוֹ
וַיִּקְרָא שְׁמוֹ פֶּלֶא יוֹעֵץ אֵל גִּבּוֹר אֲבִיעַד שַׂר־שָׁלוֹם
ki · ye·led · yu·lad la·nu, · ben · nit·tan · la·nu · va·te·hi · ha·mis·rah · al · shikh·mo
va·yik·ra · she·mo: pe·leh yo·etz · el gib·bor, · a·vi·ad · sar sha·lom
"For to us a child is born, to us a son is given; and the government shall be upon his shoulder, and his name shall be called Wonderful One, Counselor of the Mighty God,
the Father of Eternity, the Prince of Peace." (Isa. 9:5[h])
Hebrew Study Card
[Note that there is some scholarly disagreement about the grammar of this verse regarding the relationship between "pele" and "yo'etz." Some say pele should stand alone ("Wonderful One") and then "yo'etz" should be attached to "el gibbor" to form "counselor of the Mighty God," while others think that Pele and Yo'etz should go together to form "Wonderful Counselor" and "El Gibbor" should stand alone as "the Mighty God."]
Many Jewish commentators consider the promised child as Hezekiah (חִזְקִיָּהוּ), the successor to Ahaz and the Messianic hope of Israel at the time. They believe this because the verbs (yulad and nitan) are in the perfect tense (suggesting completed action). However, it should be noted that the perfect tense is likewise used in Isaiah 5:13, which states that Israel had already gone into exile when it was clear this had not occurred yet. Regardless, the hope that one of David's descendants would establish the kingdom of God upon the earth is a recurring theme in Isaiah, and Hezekiah's birth signified God's presence with Israel during a precarious time in Jewish history.
But notice that the language of Isaiah 9:6-7 refers to the ideal King of Israel (i.e., the Messianic hope) in terms that can be read as God's Presence embodied on earth. The four terms used to describe this King clearly transcend the historical person of King Hezekiah. For example, the word pele (פֶּלֶא, Wonderful One) is used in Judges 13:18 regarding the name of the Angel of the LORD (מַלְאַךְ יְהוָה), who in verse 22 is identified as God). Yoetz El Gibbor (יוֹעֵץ אֵל גִּבּוֹר, The Counsellor Mighty God) is clearly a title for the Holy One of Israel (Isa. 10:20-21; Psalm 24:8). Avi'ad (אֲבִי־עַד, the Father of Eternity) refers to God as Avinu Malkenu (see Isa. 63:16, 1 Chron. 29:10; Psalm 68:5; Mal. 2:10). And as for Sar Shalom (שַׂר־שָׁלוֹם, The Prince of Peace), both the Talmud and Scripture refer to "the Name of God as Peace" (Shab. 10b, Judges 6:24). It is clear, therefore, that these terms are designations for the LORD God of Israel and not merely that of a human being.