While we translate the word וידגו to mean "and let them grow," in reality the word emanates from the root לדוג -- "to fish." So in essence, Ya'akov blesses his grandchildren that they should become "many like the fish in the midst of the land." Why does Ya'akov use this curious language? What message does he convey by blessing his grandchildren to grow like fish?הַמַּלְאָךְ הַגֹּאֵל אֹתִי מִכָּל-רָע, יְבָרֵךְ
אֶת-הַנְּעָרִים, וְיִקָּרֵא בָהֶם שְׁמִי, וְשֵׁם אֲבֹתַי אַבְרָהָם וְיִצְחָק;
וְיִדְגּוּ לָרֹב, בְּקֶרֶב הָאָרֶץ.
the angel who has redeemed me from all evil, bless the lads; and let my
name be named in them, and the name of my fathers Abraham and Isaac; and let
them grow into a multitude in the midst of the earth.'
Rashi, basing his comments on the Gemara in Brachos explains,
Ohr Hachayim gives a different explanation. He suggests that when God creates the world, He gives special blessings to the fish to reproduce because the ocean is a particularly unhospitable place to procreate. For this reason, God increases endows the fish with special ability to thrive and multiply.
Just as the fish of the sea are covered by the water, and the 'evil eye' does
not rule over them, so too the children of Yosef - the 'evil eye' does not rule
Why then does Ya'akov give his grandchildren this special blessing of the fish? Perhaps Ya'akov foresees a day in Egypt when his descendants would no longer be able to reproduce without fear of repercussion. That day comes soon enough when the government decrees death for all infant male children, forcing the women to give birth in secret.
Indeed, Ya'akov's blessing has protected us all too often throughout our history, giving us the will and divine blessing to bring another generation of Jews into the world - sometimes despite great challenge and difficulty -- to carry on our forefather's great legacy.