What does Isaiah 26:2 mean?

Isaiah is revealing a song of praise to the Lord. This song will be sung in the land of Judah when the Lord establishes His reign as king on earth. God has destroyed the "world city" of all those on earth opposed to Him and to His people. Now the prophet sings of a new city. Rather than the worldly city which came before, this "city" is Messiah's rule on earth. His kingdom is an eternal and indestructible stronghold for the people of the Lord. Isaiah has described this city's walls as being made of salvation (Isaiah 26:1).

Now he calls for the gates of the city to be thrown open. Who may enter this holy and secure city of God? Any nation that keeps faith in the Lord may enter. Since the very beginning of Israel, the Lord has been clear that He wants His people to trust in Him completely. It was said of Abram that the Lord counted the man's belief in Him "as righteousness" (Genesis 15:6). Paul amplified this great truth in Romans 4, showing that Abraham was declared righteous not because of his works, but because of his faith.

Every nation that is righteous can enter the Lord's holy city. In these contexts, to be "righteous" does not mean sinless perfection. Instead, it means those who keep faith in the Lord. As Paul shows, that faith in the one who raised Jesus from the dead is the only way to find forgiveness from sin and to be justified by God (Romans 4:24–25).