A esta

A esta
 

A esta receta le falta un ingrediente principal. This recipe lacks a main ingredient.

A este pobre le falta una pierna. This poor man is missing a leg.

Came across these at Ask.com. The "A" in the second seems OK but why in the first?

Por siempre, gracias. Bob

"A esta receta" and "a este pobre" are indirect objects. "Personal a" is specific to direct objects.

Besides being indirect objects, they are prepositional phrases (that's why they start with the preposition 'a'). ;)

A personal 'a' is used in a direct object when the direct object is a person, as wrholt said, but there is yet another 'a' used in the direct object that is not called a personal 'a'. It is the preposition 'a', used to distinguish the direct object from the subject when there could be some doubt as to what role the noun plays. Look here.