with the intent that he return it. The father must give it to the Cohen with the resolution that he is giving him a present without any reservations. Cohens and Levites are exempt from the redemption of their firstborn, as they served as the redemption of the Israelites' firstborn in the desert. One born to a woman of a priestly or Levite family is exempt, for the matter is dependent on the mother, as indicated by and . A baby born by Caesarian section and any subsequent birth are exempt: the first because it did not emerge from the womb, and the second, because it was preceded by another birth. The obligation for redemption takes effect when the baby completes 30 days of life, as says, "And those to be redeemed should be redeemed from the age of a month." In modern interpretation The parashah is discussed in these modern sources: Exodus chapter 10 Greta Hort argued that the plagues concentrated within a period of about 12 months, based on the report of that Moses was 80 years old when he first spoke with pharaoh and the report of that Moses was 120 years old when he died, after spending 40 years in the wilderness. John J. Collins reported that some scholars have suggested that the plague stories contain a reminiscence of a mid-fourteenth century BCE epidemic referred to as "the Asiatic illness." Collins argued that the plague stories show that Exodus is not only the story of the liberation of Israel, but also of the defeat and humiliation of the Egyptians, and thus involved "less than edifying" nationalistic, ethnic vengeance. Everett Fox noted that "glory" (, kevod) and "stubbornness" (, kaved lev) are leading words throughout the book of Exodus that give it a sense of unity. Similarly, William Propp identified the root kvd—connoting heaviness, glory, wealth, and firmness—as a recurring theme in Exodus: Moses suffered from a heavy mouth in and heavy arms in ; Pharaoh had firmness of heart in ; , 28; , 34; and ; Pharaoh made Israel's labor heavy in ; God in response sent heavy plagues in ; , 18, 24; and , so that God might be glorified over Pharaoh in , 17, and 18; and the book culminates with the descent of God's fiery Glory, described as a "heavy cloud," first upon Sinai and later upon the Tabernacle in ; ;