Theory:

Our lays are of cities whose lustre is shed,
The laughter and beauty of women long dead;
The sword of old battles, the crown of old kings,
And happy and simple and sorrowful things.
Explanation:
  
The wandering singers adopt themes for their songs about cities whose glorious past have been forgotten; about the past lives of noble, happy and beautiful women; about mighty battles and the kings who fought with bravery; finally they also sang about happy, simple and sorrowful day-to-day matters that touched everyone's hearts.
 
songs.jpg
Themes included ancient cities, noble women, glorious sword battles, happiness and sorrow!
 
The poet conveys that their songs covered many subjects like beauty, history, glory, bravery, happiness and sorrow.
 
Meanings of difficult words:
  
No.
Words
Meanings
1
laysshort songs or lyrics or narrative poems meant to be sung
2
lustrea  gentle shine or soft glow
3
sorrowfulcausing grief
Reference:
State Council of Educational Research and Training (2019). Term-2 English Standard-7. Wandering Singers - Sarojini Naidu (pp. 122-125). Published by the Tamil Nadu Textbook and Educational Services Corporation.