What does Isaiah 4:3 mean?
This part of Isaiah's prophecy appears to describe the nature of the "remnant." This refers to the people who will occupy Zion and the city of Jerusalem during the time when the Messiah reigns on earth. That remnant of believing Israelites , who are referenced in Romans 9, will be referred to as "holy".Isaiah is showing the contrast between the wickedness of the people of Judah during his own time and the completely holy nature of God's people in this future moment. These Israelites, living in submission to the Messiah will be a holy people. Which is what the Lord always intended for Israel.
To be holy is to be set apart by God for His special purpose. God is the final definition for what is holy, meaning that to be holy is also to be like God. The history of Israel as recorded in the Old Testament is evidence that human beings cannot simply choose to be holy. All of us sin and fall far short of that standard (Romans 3:23). To become righteous before God, the children of Abraham had to, ,and will have to, put their faith in the Messiah (Romans 4:13). Then they will be declared holy, living under His branch in Zion.