וְאֵ֤ל שַׁדַּי֙ יְבָרֵ֣ךְ אֹֽתְךָ֔ וְיַפְרְךָ֖ וְיַרְבֶּ֑ךָ וְהָיִ֖יתָ לִקְהַ֥ל עַמִּֽים׃
願全能者上帝賜福給你，使你生養眾多，使你繁衍增多，好讓你成為眾民的會眾。
Rashi
ואל שדי AND GOD ALMIGHTY —He who has a sufficiency of blessings שָׁדִּי for those who are blessed by Him, יברך אתך MAY HE BLESS THEE.
Chizkuni
ואל שדי, “and the G-d known also as Shaddai;” the G-d Who has said of Himself that none of His creatures needs any other power to help him. (Compare Rashi on Genesis 17,1) “He will bless you.”Rabbi Eleazar in Bereshit Rabbah 67,12, says that a divorce decree becomes valid only after its signatories have appended their seals to it. This is why Yitzchok was not content with the blessing he had already given Yaakov which had commenced with the words: ויתן לך, in 27,28.