בַּיּ֣וֹם הַה֔וּא יוּשַׁ֥ר הַשִּׁיר־הַזֶּ֖ה בְּאֶ֣רֶץ יְהוּדָ֑ה עִ֣יר עָז־לָ֔נוּ יְשׁוּעָ֥ה יָשִׁ֖ית חוֹמ֥וֹת וָחֵֽל׃
In that day shall this song be sung in the land of Judah: We have a strong city; Walls and bulwarks doth He appoint for salvation.
Read kabbalistic (mystical) interpretation of Isaiah 26:1: and classical mystical sources.