What does Isaiah 4:2 mean?

Isaiah is concluding a section that began in Isaiah 2:1–4. In those verses he looked far into Israel's future and pointed to a time when people from all the nations of the earth would come to the mountain of the Lord to learn from the God of Jacob. He was looking toward Christ's reign as king over all the earth.

He turned then to describe the time he lived in and what was coming for Israel (Isaiah 2:12–19). God would soon judge His people for their failure to trust in Him alone. This was demonstrated in their worship of false gods and mistreatment of the poor (Isaiah 2:8,3:13–15). He would take away everything they once held dear instead of trusting in Him (Isaiah 3:1–3, 18–24). This judgment would end with the destruction of Jerusalem by foreign invaders who decimated the city, leaving only a small remnant behind (Isaiah 3:25–26). The aftermath for those survivors would be brutal.

Now, Isaiah is going back to describing that far-off time in Israel's future when the Messiah will reign over the earth from Jerusalem. Isaiah begins Isaiah 4:2 by saying "in that day," likely referring to the same "latter days" from Isaiah 2:2 following another time of judgment and hardship for Israel.

Most scholars, but not all, agree that the branch of the Lord is a reference to the Messiah. Isaiah will have recurring references to the Messiah throughout his text. This Messiah is none other than Jesus Christ the Lord, the Son of God and true hope of Israel, who referred to Himself as the Vine (John 15:1). He is the "branch of the Lord," sprung up from the root of the line of King David, the "root of Jesse" (Isaiah 11:1, 10). But the branch is also the fruit of the land of Israel, it's final and most important product and export.

The Messiah and this "fruit of the land" will be the esteem of the survivors of Israel. This is the remnant of survivors Isaiah described in Isaiah 1:9, and it also may represent the remnant of Israelites who come to trust in Jesus, as described by Paul in Romans 9.