en_tn_condensed/isa/63/11.md

They said

"we said." Here "they" refers to the people of Israel. Isaiah included himself as a member of the people.

who brought them up out of the sea

The story of Yahweh miraculously splitting the waters of the Sea of Reeds so that the Israelites could cross and escape the Egyptians is assumed knowledge. (See: rc://en/ta/man/translate/figs-explicit)

the shepherds of his flock

Leaders are sometimes referred to as "shepherds." Alternate translation: "the leaders of his people" (See: rc://en/ta/man/translate/figs-metaphor)