“But you must surely redeem the firstborn of man!” (Bamidbar 18:15)
It is a positive commandment that one must redeem the firstborn of a person. This means to say that any man from Klal Yisrael who has a child who is the firstborn to its Jewish mother has a commandment that the father must redeem him, as it says “But you must surely redeem the firstborn of man!”, and in another place the Torah specified that this refers to the firstborn of the mother, as it says “Any firstborn who is the opener of the womb amongst the children of Yisrael, amongst the people and the animals, it is mine!”.
Amongst the roots of this commandment are that Hashem wanted to give people the merit to fulfil His commandments with the first of their children, so that they will know that everything is His, and a person has nothing in this world apart from that which Hashem, in His kindness, has given him. He must understand this, when he sees that after a person has made a lot of effort and worked very hard in this world, and the time has arrived when it bears fruit, and his firstborn is cherished like the apple of his eye, he must give it immediately to Hashem. Furthermore, this is to remind us of the great miracle that Hashem did for us with the Egyptian firstborns, when He killed them and saved us from their hands.
Amongst the laws of this commandment are that the commandment of redeeming is after thirty days or more have passed over the child. This commandment is incumbent on the father, but if the father did not redeem him, it is the obligation of the son to redeem himself after he grows up. The method of redemption is by giving five Sela’im (Silver coins) to the priest. One may give all five to the same priest, or divide them amongst many priests. The redemption takes place by giving to a male priest. If the priest wants to return the money after the redemption, he may do so, so long as the money was not given with the condition that he must return it to him. If he gave it on condition that he must return it, the redemption is not valid.
This commandment applies in all places and at all times, to male Jews. The mother is not obligated to redeem her son. It does not apply to priests and Levites, and even if the father is Jewish and the mother comes from a family of priests or Levites, the son does not need to be redeemed. One who does not redeem his firstborn son after he is thirty days old, and dies without having redeemed him, has transgressed this commandment. Even though there is no fixed time for this commandment, as any time is good for the fulfilment of this commandment, nevertheless a man wise of heart will gather commandments, and do them as early as he can, and with the will of Hashem he will succeed. The father is obligated to redeem his son even after he grows up.