Genesis 17:9-14; 23-27 NIV
 Then God said to Abraham, “As for you, you must keep my covenant, you and your descendants after you for the generations to come.  This is my covenant with you and your descendants after you, the covenant you are to keep: Every male among you shall be circumcised.  You are to undergo circumcision, and it will be the sign of the covenant between me and you.  For the generations to come every male among you who is eight days old must be circumcised, including those born in your household or bought with money from a foreigner-those who are not your offspring.  Whether born in your household or bought with your money, they must be circumcised. My covenant in your flesh is to be an everlasting covenant.  Any uncircumcised male, who has not been circumcised in the flesh, will be cut off from his people; he has broken my covenant .”
 On that very day Abraham took his son Ishmael and all those born in his household or bought with his money, every male in his household, and circumcised them, as God told him.  Abraham was ninety-nine years old when he was circumcised,  and his son Ishmael was thirteen;  Abraham and his son Ishmael were both circumcised on that very day.  And every male in Abraham’s household, including those born in his household or bought from a foreigner, was circumcised with him.
You can't do better than starting a new week of Bible readings with a devotion about circumcision! Seriously, I have asked myself many times: of all the marks or rites of identification that God could have chosen to signify His covenant with His people, why did He choose this? A t-shirt or a tattoo or a special necklace would have sufficed!
Male circumcision was actually a common practice among Middle Eastern peoples, but it was generally applied to boys on the verge of adulthood, not at birth. Applying it when they are born reflects the fact that they do nothing to earn it. They were accepted by God and became part of the covenant through no merit of their own. However, as they grew older and grew to understand the implications of being part of God's family, it was then up to them to live out their side of the covenant agreement through obedience and faith.
In a similar way, as was once the custom in Britain, my parents had me baptised when I was a baby, even though they had little involvement in church at this time. I don’t know if they fully understood what baptism was about - they just felt it was important to get the child "done" in case anything bad should happen. It was the cultural thing to do in what was considered a 'Christian country'. Later on in life, I had to personally declare the promises they made on my behalf for them to be effectual in my life. I committed to follow Jesus for myself, I renounced the devil and all his works and became part of the church.
Like Christian baptism (or communion), circumcision was an outward sign of an inward devotion. In itself it carried no power or effect - rather it pointed to something beyond and deeper than the physical, outward act.
Unfortunately many within my tradition of Anglicanism still believe that baptism is what makes one a Christian rather than personal faith in Jesus. The same happened in Judaism. By the time of Jesus, about two thousand years after Abraham, many Jewish religious leaders taught that circumcision automatically made a boy righteous in God’s eyes.
The apostle Paul set the record straight: physical circumcision is just a symbol of a man’s desire to keep the covenant. It cannot replace a personal relationship with God any more than a wedding ring can substitute for a marriage. In our culture, one wears a ring on the third finger of the left hand as a sign of being faithfully married to a spouse. If you’re a cheating spouse, your ring is a lie. Likewise, Paul writes that “a true Jew is one whose heart is right with God. And true circumcision is not merely obeying the letter of the law; rather, it is a change of heart produced by God’s Spirit.” (Romans 2:29).
One other comment here: circumcision was something no one except God and the one circumcised would see. However, if done with genuine faith and devotion to God, that which was done in private would bring blessing from God in public. The painful cutting off of things they deeply valued would bring great reward and favour from Yahweh.
God at times calls all of us to "cut away" things from our lives. It could be things which are hindering our spiritual life, good things which have become 'god things', idols which steal our devotion to Christ; relationships, hobbies or material things which have too much of our hearts. This cutting, or 'pruning' as Jesus calls it in John 15, is painful, at least in the short term. It is spiritual surgery, often done unseen, in private; it is just between us and God. However our obedience to the whisper of the Spirit, our sacrifice and surrender, will be noticed by Heaven. The result of such pruning, according to Jesus, is that we will 'bear much fruit' which likely will be visible and public. In God's Kingdom, private devotion brings public rewards.
"Then your Father, who sees what is done in secret, will reward you." (Matt 6: 6)
"....what you have whispered in the ear in the inner rooms will be proclaimed from the roofs." (Luke 12: 3)