Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:4/4
K:A
['', 'eA (3AAA cAec', 'ae faec']  
X:1
L:1/8
M:4/4
K:A
 cd |: eA (3AAA cAec | dB (3BBB a2 fa | eA (3AAA cAec | dfed cAcd :: ea ae faec | B2 bage fg | 
 a2 ae faec | dfed cAcd :|  