A mother's firstborn Jewish male child must be redeemed from a Kohen (priest) for 5 biblical silver shekels, containing a total of at least 109 grams of pure silver.
The redemption of firstborn sons stems from the fact that, from the moment the portable Temple was completed in the desert, the firstborn were required to dedicate themselves to Temple service. However, the involvement of all tribes except Levi in the sin of the Golden Calf deprived the firstborn of the opportunity to serve in the Temple. The tribe of Levi was dedicated to Temple service. However, the total number of firstborn sons exceeded the number of Levites, and a ransom was required to exempt the firstborn from Temple service, which was then given to the Kohen (priest). Therefore, the commandment of "pidyon ha-ben" (redemption of the firstborn) does not apply to firstborn sons whose mother or father belonged to the Levite or Kohen lineage.
The firstborn son of a father is entitled to double the share of the inheritance compared to other sons.