ה֣וּא יִ֭קְרָאֵנִי אָ֣בִי אָ֑תָּה אֵ֝לִ֗י וְצ֣וּר יְשׁוּעָתִֽי׃
ער װעט מיך רופֿן: מײַן פֿאָטער ביסטו, מײַן גאָט, און דער פֿעלדז פֿון מײַן הילף;
Rashi
begotten you to be called My son and to be beloved to Me as a son for their sake, as it is stated (I Chronicles 14:2): ‘And David knew that the Lord had established him as king over Israel, and that his kingdom was highly exalted for the sake of His people Israel.’ And we find that the kings of Israel who were beloved before Him were called sons, as it is stated (II Sam. 7:14) concerning Solomon: “I will be to him a father, and he shall be to Me a son.” We find further concerning David (Ps. 89:27) “He shall call Me, ‘You are my Father, my God, and the Rock of my salvation.’”
Ramban
FOR THERE WAS NOT A HOUSE WHERE THERE WAS NOT ONE DEAD. Rashi comments: “If there was a firstborn there, he died; if there was no firstborn there, the chief person in the house died because he is called b’chor (firstborn), as it is said, I also will appoint him firstborn.275Psalms 89:27. Another interpretation: The Egyptian women led dissolute lives under their husbands and bore children from unmarried young men. Thus they had many firstborn sons, sometimes [as many as] five to one woman, each one being the firstborn to his own father.”
In line with the plain meaning of Scripture, the firstborn that died in Egypt were the firstborn of their mothers, and this is why He sanctified in their place all the firstborn, whatsoever openeth the womb among the children of Israel, both of man and of beast.276Further, 13:2. The firstborn of Pharaoh that sat on his throne277Verse 29. was the firstborn to his mother. And such indeed is the custom among kings that the reigning mistress be a virgin, something like it is said in the case of Ahasuerus.278Esther 2:3. But in accordance with the opinion of our Rabbis [who say that the firstborn of a father also died], we shall explain that in Egypt, He smote all their firstborn. That is to say, the firstborn of the father, since he is the first-fruit of his strength,279See Genesis 49:3. and the firstborn of the mother, since he opened the womb, and also the chief person in the house. Yet it was His desire to sanctify in Israel in their place only the firstborn of the mother, because that is a matter more known and of open knowledge. In cattle, only the firstborn of the mother is known at all, and therefore He chose from among all of them only [the firstborn of the mother]. A sort of proof for this [statement of the Rabbis that the firstborn of the father was also smitten] is the verse: And He smote all the firstborn in Egypt, the first-fruits of their strength in the tents of Ham,280Psalms 78:51. for such an expression, [i.e., the first-fruits of his strength], is said only of a male.
In line with the plain meaning of Scripture, the firstborn that died in Egypt were the firstborn of their mothers, and this is why He sanctified in their place all the firstborn, whatsoever openeth the womb among the children of Israel, both of man and of beast.276Further, 13:2. The firstborn of Pharaoh that sat on his throne277Verse 29. was the firstborn to his mother. And such indeed is the custom among kings that the reigning mistress be a virgin, something like it is said in the case of Ahasuerus.278Esther 2:3. But in accordance with the opinion of our Rabbis [who say that the firstborn of a father also died], we shall explain that in Egypt, He smote all their firstborn. That is to say, the firstborn of the father, since he is the first-fruit of his strength,279See Genesis 49:3. and the firstborn of the mother, since he opened the womb, and also the chief person in the house. Yet it was His desire to sanctify in Israel in their place only the firstborn of the mother, because that is a matter more known and of open knowledge. In cattle, only the firstborn of the mother is known at all, and therefore He chose from among all of them only [the firstborn of the mother]. A sort of proof for this [statement of the Rabbis that the firstborn of the father was also smitten] is the verse: And He smote all the firstborn in Egypt, the first-fruits of their strength in the tents of Ham,280Psalms 78:51. for such an expression, [i.e., the first-fruits of his strength], is said only of a male.