|Circumcision of Christ by Bellini|
According to the Law of Moses, male children were required to be circumcised 8 days after their birth (Book of Leviticus, chapter 12 verses 2 - 3), a rite extending all the way back to the time of father Abraham (Book of Genesis, chapter 17 verses 9 - 14). Circumcision was one of the works of the law, along with Sabbath observance and the food laws, that marked you out as a member in good standing of God's covenant with Israel.
Jesus' parents made sure that he was raised as a faithful son of the Covenant, starting with this.
When eight days had passed, Jesus’ parents circumcised him and gave him the name Jesus. This was the name given to him by the angel before he was conceived. When the time came for their ritual cleansing, in accordance with the Law of Moses, they brought Jesus up to Jerusalem to present him to the Lord. (It’s written in the Law of the Lord, “Every firstborn male will be dedicated to the Lord.”) They offered a sacrifice in keeping with what’s stated in the Law of the Lord, A pair of turtledoves or two young pigeons.(Gospel of Luke, chapter 2 verses 21 - 24, Common English Version)
About 50 years after this event transpired, Paul of Tarsus explained its significance:
When we were minors, we were also enslaved by this world’s system. But when the fulfillment of the time came, God sent his Son, born through a woman, and born under the Law. This was so he could redeem those under the Law so that we could be adopted. Because you are sons and daughters, God sent the Spirit of his Son into our hearts, crying, “Abba, Father!” Therefore, you are no longer a slave but a son or daughter, and if you are his child, then you are also an heir through God.(Letter to the Galatians, chapter 4 verses 3 - 5, CEB)
As the Messiah Jesus lived in faithful obedience to the covenant God made with Moses and the ancient nation of Israel. And as Messiah he had the authority to institute a new covenant that superseded the previous one and freed his people "from all those sins from which you couldn’t be put in right relationship with God through Moses’ Law," (Acts of the Apostles, chapter 13 verses 38 - 39, CEB). What marks you out as a member in good standing of this covenant is not circumcision but trust in and allegiance to Jesus of Nazareth. And the sacrifice is the Messiah himself.
So this ancient, bloody, painful little ritual had cosmic significance that day in 4 BC. Some theologians even see it as a downpayment of the blood Christ would pour completely out 33 years later on the cross. Joseph and Mary just saw their young son enduring his first experience with suffering in obedience to God.