Tikva & Mikva

Ezra cried out bitterly over the fact that the Jews intermarried and assimilated during the Babylonian exile. After they returned to the Holy Land they wanted to repent. The leaders came to Ezra saying, "But surely there is mikva, hope!" (Ezra 10:2). The usual word for hope is tikva, but the verse intentionally uses the word mikva (מִקְוֶה) to teach us that no matter how serious a person's transgressions, there is always hope: the mikva has the power to bring one to complete repentance.

(Reb Nosson of Breslov)