Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/8=100
M:4/4
K:D
['FG A2 B3 d', 'D4 f4 g4 ecBA dAGF GABG AGFE']  
X:1
L:1/8
Q:1/8=100
M:4/4
K:D
 FG A2 B3 d | eABc d2 ef | g3 g fedf | ecBA BA G2 | FG A2 B3 d | ecef g3 g | fedA BcdF | E4 D4 || 
 f4 g4 | ecBA dAGF | GABG AGFE | EFED D4 | FG A2 Bc d2 | efgf f3 a | g3 b agfe | efed d4 ||  