Matt 1:22 Now all this took place to fulfill what was spoken by the Lord through the prophet:

Matt 1:22 Now all this took place to fulfill what was spoken by the Lord through the prophet:

Why does all this take place?

"Now all this took place to fulfill what was spoken. . ." (Matt 1:22).

Who spoke what is being fulfilled?

". . . what was spoken by the Lord. . ." (Matt 1:22).

Through whom does the Lord speak what was spoken?

". . . through the prophet" (Matt 1:22).

The prophet who is quoted in the following verse is Isaiah, an eighth-century BC royal prophet of unparalleled renown whose writings have been referred to as The Fifth Gospel because of their remarkable revealing of the Person and work of the Messiah. The book of Isaiah is dated by conservative scholarship to be no later than about 700 BC (Eugene Merrill, Everlasting Dominion, 501). Isaiah’s oracles address both a present and future audience regarding Judah’s idolatry, imminent exile and future restoration to the land. Beyond the address to ancient Judah, Yahweh outlines the broad eschatological scope of his plan to redeem and establish his kingdom under the reign of the Messiah. Isaiah delivers messages that apply to contemporaneous and eschatological events.
Isaiah records the deaths of Ahaz (Isa 14:28) in 715 BC and Sennacherib (Isa 37:88) in 681 BC, which indicates that the prophet outlived Hezekiah. Legend purports that Isaiah was sawn in two during the reign of Manasseh (696–642 BC) (date of Manasseh's reign reported by William Schlegel, Satellite Bible Atlas, 2013, 149). The biblical account verifies the violence of Manasseh, “Moreover, Manasseh shed very much innocent blood until he had filled Jerusalem from one end to another . . .” (2 Kgs 21:16). Hebrews 11 confirms that the prophets “were stoned, they were sawn in two . . .” (Heb 11:37).  A chronicle of Isaiah's death is recorded in a Jewish apocryphal work, Martyrdom and Ascension of Isaiah, which was familiar to the Church Fathers:

"Because of these visions, therefore, Beliar was angry with Isaiah, and he dwelt in the heart of Manasseh, and he sawed Isaiah in half with a wood saw. And while Isaiah was being sawed in half, his accuser, Belkira, stood by, and all the false prophets stood by, laughing and (maliciously) joyful because of Isaiah. And Belkira, through Mekembekus, stood before Isaiah, laughing and deriding. And Belkira said to Isaiah, ‘Say, “I have lied in everything I have spoken; the ways of Manasseh are good and right, and also the ways of Belkira and those who are with him are good.”’ And he said this to him when he began to be sawed in half. And Isaiah was in a vision of the LORD, but his eyes were open, and he saw them. And Belkira spoke thus to Isaiah, ‘Say what I say to you, and I will turn their heart and make Manasseh, and the princes of Judah, and the people, and all Jerusalem worship you. And Isaiah answered and said, ‘If it is within my power to say, ‘Condemned and cursed be you, and all your hosts, and all your house!’ For there is nothing further that you can take except the skin of my body.” And they seized Isaiah the son of Amoz and sawed him in half with a wood saw. And Manasseh, and Belkira, and the false prophets, and the princes, and the people, and all stood looking on"  [James H. Charlesworth, ed. The Old Testament Pseudepigrapha, 2 vols., vol. 2 , 163-64.]

If accurately reported, the account reflects the tumultuous political turmoil of Isaiah’s day and the dark depravity of Manasseh’s reign that ushers in the judgment of Judah into Babylonian exile. Against the backdrop of impending judgment, Yahweh reveals details of the Messiah that would be realized in the birth, ministry, and suffering of Jesus, whose incarnation was foretold by the Lord through the prophet Isaiah over seven hundred years before His birth.

Adonai,

You are the God who breathes prophecy into existence and fulfills it. Your glory is revealed as You watch over Your Word to fulfill it.

How brilliantly Your power is revealed through messianic prophecy and its fulfillment in the incarnation of Your Son Who came in the flesh and dwelt among us. In Jesus, Your glory is revealed, Your Word is fulfilled, and salvation comes to the ends of the earth to save your people from their sins. In Jesus, grace and truth are revealed. And in Him we are blessed with grace upon grace. New birth by the Spirit into Jesus brings life that is abundant and free, for whom the Lord sets free is free indeed, to the praise of Your glory. In Jesus' Name, Amen.