"Come now, let us reason together, says the LORD: though your sins are like scarlet, they shall be as white as snow; though they are red like crimson, they shall become like wool" (v. 18).
The writers of Scripture always structure their books for a purpose. Yet Isaiah's arrangement of his material has puzzled many scholars, particularly because he does not narrate his prophetic call until chapter 6. Seeing chapters 1–6 as an introduction to the entire book, however, helps us make sense of Isaiah's intent. Isaiah 1–5 outlines the endemic problems of eighth-century-BC Judah—idolatry, injustice, and distrust of God. These conditions troubled the faithful in the southern kingdom, who asked, "What should God's people do as society crumbles?" Isaiah 6 answers: like Isaiah, the righteous must trust the Lord who judges in holiness and preserves a righteous remnant for Himself. These themes are then explored throughout the rest of Isaiah.
Because chapters 1–6 introduce the book thematically, Isaiah does not necessarily present the oracles of these chapters in chronological order. Instead, it seems Isaiah draws oracles from different points in his ministry, setting the stage for the teaching of his entire book. Judah heard bad news when Isaiah preached the oracles in this introduction— destruction was coming for the nation's sin. The sin that birthed all of Judah's evil was the nation's failure to know God. Since even animals know their owners, the people of God in the territory of Judah—the children of Israel (Jacob)—should have known their covenant Lord, but, in Isaiah's day, the nation as a whole did not (Isa. 1:2–3).
Unsurprisingly, idolatry was a key problem. The people "desired" oaks and chose gardens (v. 29). The reference here is likely to sacred groves of trees and gardens that were associated with the cults of Baal and Ashoreth, fertility religions of the ancient Near East that often enticed God's people (Judg. 3:7). When the people did worship the one true God, Yahweh, their rituals were empty and not from the heart (Isa. 1:11–14). Ethically, Judah was particularly sinful as well. The people had to be told to seek justice for orphans and widows, and to help the oppressed (vv. 16–17). Things were so bad that Isaiah saw what the logical outcome would be without repentance—desolation (vv. 7–8).
Yet God was not going to condemn His people to exile without reasoning with them. He sent Isaiah to present the Lord's case against Judah and call the people to their senses. Through Isaiah, God called the Judahites to reason with Him, to know that His mercy could cleanse their sin fully—but only if they were to amend their ways (v. 18).
Coram Deo
Isaiah 1:18 is a great promise indeed, assuring us that no matter how much sin has stained our souls, God can cleanse us completely and make us stand before Him as His holy people. But for this to happen, we must repent. We must agree with the Lord's evaluation of sin in our lives—that it deserves His wrath—and then we must renounce it, asking for God's pardon and strength that we might resist temptation. We do this not just once but every day of our lives.