en_tn_condensed/isa/26/01.md

In that day

"At that time"

this song will be sung in the land of Judah

This can be stated in active form. AT: "the people in the land of Judah will sing this song" (See: rc://en/ta/man/translate/figs-activepassive)

We have a strong city

This refers to the city of Jerusalem.

God has made salvation its walls and ramparts

God's power to protect and save his people is spoken of as if his salvation were walls around a city. (See: rc://en/ta/man/translate/figs-metaphor)