Question

why did lencho come early to the post office​

Answer 1

Lencho came earlier to the post office to know if there was a letter for him. (b) Lencho was angry when he counted money as it was not the full amount that he had demanded from God.

Answer 2

Lencho came early to the post office because he was sure God would have replied to his letter and sent him the needed money in the letter. He had unshakable faith in God.  

As he had expected, he was handed a letter by the postman. Lencho did not show any surprise at it. He went to a corner, opened the letter and counted the money. He was disappointed to find only 70 pesos. He thought the post office employees must have taken 30 pesos from the letter.