Isaiah 38:20

Perhaps a liturgical appendix, adapting the psalm for congregational use. Hence the transition from 1st pers. sing, to 1st pers. plu.

we will sing … instruments Rather, we will play with string music ("we" including the Levites or the congregation). The word for "string music" is Něgînôth, which occurs frequently in the headings of the Psalms. Here and in Habakkuk 3:9 it has the suffix of 1st pers. sing. ("my"), which it is very difficult to explain.