There is a Mitzvah for a father to redeem his firstborn son by giving five silver coins to a Kohen. The family makes a celebration for the occasion.
“...In response to his invitation to the Pidyon Haben (redeeming of the son) of his son...
...The idea of redeeming the son...is in exchange for G-d redeeming the Jewish firstborns when He struck every firstborn in the land of Egypt and our Sages said...’Be like Him; just as He is gracious and merciful, so too you be gracious and merciful’...this is the work of every single Jew, whoever can, to save the Jewish boys and girls, about all of whom it is said, ‘My firstborn son, the Jewish People’, that they shouldn’t assimilate among the nations, may G-d save us, rather to connect them to the words of the living G-d through the Torah of life...”
(From a letter of the Lubavitcher Rebbe King Moshiach Shlita, Igros Kodesh vol. 2, pg. 161)
