the ” horse ” is a symbol for what i want to be , my goal

asnwer:

when stating something about oneself, usually the watashi is omitted.
何時かは馬になるだ。そして欲しいの物になります。
itsuka wa uma ni naru da. soshite hoshii no mono ni narimasu.

itsuka — sometime, someday, one day
wa — topic marker
uma — horse
naru — to become
da — plain copula
soshite — and, and then
hoshii — want
no — possessive particle
mono — (tangle-able) thing
ni — in, on, at / target particle
narimasu — (-masu form of naru)