The phrase mikveh yisra’el is well-known in later Jewish history. In many places there are synagogues with this name. Manasseh ben Israel wrote a famous book with this title.
Before we look at the idea of God as the Hope of Israel, let us comment on the thought of God as Israel’s metaphorical mikveh, cleansing Israel of sin; Rabbi Akiva said, “Happy are you, O Israel! Before whom are you cleansed, and who cleanses you? Your Father in heaven!” (Mishnah Yoma 8:9). If we sin and then repent, God washes away our wrongdoing.
The Psalmist tells us, kavveh el HaShem, “hope in the Lord” (Psalm 27:14). Kavveh and mikveh are clearly connected. Kavveh as “hope” has been explained as deriving from kav, a line – hence the Psalmist may be saying, “Throw a line to God – remain linked with the Almighty whatever happens, and He will pull you to safety”.
The common Hebrew word for hope is tikvah, from the same root. The anthem Hatikvah, “The Hope”, proclaims that the line that joined the people of Israel to their land never frayed or broke despite all the years of persecution and suffering.
A quite different possibility is reported by Rabbi Harry Freedman in his commentary in the Soncino edition of Jeremiah. “Comparing a cognate Arabic noun,” he says, “Ehrlich suggests that the meaning of mikveh is ‘might'”. If this view holds water, it means that the verse is to be rendered, “O Mighty One of Israel, the Lord!”