This is what the rabbi of Kotzk said concerning Rabbi Akiba's saying that "God is the waters of immersion of Israel": "The waters of immersion only purify the soul if one is wholly immersed, so that not a hair is showing. That is how we should be immersed in God." -- Martin Buber, Tales of the Hasidim: The Later Masters
אמר רבי עקיבא אשריכם ישראל לפני מי אתם מטהרין מי מטהר אתכם אביכם שבשמים שנאמר (יחזקאל לו, כה) וזרקתי עליכם מים טהורים וטהרתם ואומר (ירמיהו יז, יג) מקוה ישראל (ה') מה מקוה מטהר את הטמאים אף הקב"ה מטהר את ישראל
Rabbi Akiva said: How fortunate are you, Israel; before Whom are you purified, and Who purifies you? It is your Father in Heaven, as it is stated: “And I will sprinkle purifying water upon you, and you shall be purified” (Ezekiel 36:25). And it says: “The ritual bath of Israel is God” (Jeremiah 17:13). Just as a ritual bath purifies the impure, so too, the Holy One, Blessed be He, purifies Israel.
O Hope ("mikveh") of Israel! O LORD! All who forsake You shall be put to shame, those in the land who turn from You shall be doomed men, for they have forsaken the LORD, the Fount of living waters.