The form ест ((s)he eats) is always third person present singular from the verb есть and so forever shall it be. It is therefore very different from the form есть.
(Yes, the palatalisation (that nowadays unpronounced soft sign at the end of the verb) does matter in Russian phonetics).
But, again, the form есть is a homonym of
a) the infinitive form of есть (to eat) and
b) the third person present singular copula verb есть ('to be', but also used as 'to have' in 'A has B'-type structures.
So, in fact, you have to distinguish between all three (unless you also want to know why in certain structures of the A-has-B-type, Russian speakers prefer to use this form, and in other cases of the same structures, they omit the verb completely, e.g. what's the difference between the phrases 'У меня есть машина'; 'У меня - машина' and 'Машина - у меня').
