How do we know that Hashem will receive and accept our teshuva?

The Ba’al HaTanya (Rabbi Schneur Zalman of Liadi) explains in Igeret Ha’Teshuva that we say, in the Shemonei Esrei (the 18 blessing prayer), three times each day:

“Forgive us our Father for we have sinned, pardon us for we have transgressed.

Blessed are You Hashem, the gracious one who always forgives in an abundant fashion.”

We say this day after day, week after week, month after month, year after year.

Maybe Hashem doesn’t forgive after doing the same sin so many times? Are we making a blessing in vain?

The Ba’al HaTanya says that if we had even a slight doubt that Hashem will forgive us, we would not be allowed to say this blessing every Shemonei Esrei as it would be a blessing in vain, which is forbidden.

This teaches us that it is never a question from a Torah perspective. The moment someone says that they are sorry and they are sincere, Hashem forgives completely.

How? A finite human being has a finite amount of love. He will not be able to forgive someone who offends him multiple times. But Hashem’s love is Infinite. The moment a person shows up and wants to be back in the relationship with Hashem, he is accepted.