"Zeh Keli V’Anvayhu" (Perek Tes Vov Pasuk Bais). After Bnei Yisrael successfully cross the Yam Suf, their joy is so great that they begin to sing Shirah -- "Az Yashir Moshe U’Bnei Yisrael." The beginning of the Shirah is full of praise for Hashem. "Zeh Keli V’Anvayhu," this is my G-d and I will exalt him. "Elokei Avi V’Aromimenhu," the G-d of my father and I will ascribe Him to exaltation."
Rashi Hakadosh explains on the words "Elokei Avi," that "Lo Ani Techilas HaKedusha." It is important for us to remember that we are not the beginning of the sanctity. We were not the first recognize Hashem. Our fathers and grandfathers before us recognized the Kedusha. This form of Anavah -- humbleness is a very important Avodah to work on, especially for Baalei Teshuvot, who may be the first in their families to recognize the Malchos of Hashem. The middah of Anavah -- humbleness is greatly treasured by the Ribbono Shel Olam.
The Gemara in Shabbos - Daf Kof Gimmel -- explains that the word "Anvayhu" is "Ani" "V’hu" -- me and Hashem. The Gemara also relates that concerning a Baal Gavah - someone who holds themselves in high-esteem, Hashem has said "Ayn Ani V’hu Yochel L’Dor B’Makon Echad." Hashem cannot live in the same place as one who thinks highly of himself.
So "Zeh Keli V’Anvayhu" - when can we not only exalt Hashem, but be one with Him - only when we recognize "Elokei Avi" - that our fathers knew Him first. Only when we are humble and modest will Hashem allow us to live amongst Him.
This is what happened at Krias Yam Suf - Bnei Yisrael became one with Hashem because they acknowledged what had been before them. They recognized that their fathers and grandfathers had been amongst the first to recognize the Gadlus of Hashem.