So circumcision is a valid law that should be followed today?
Ah, you have asked an excellent question, do you not know what the "shadows of the law are"?
Therefore do not let anyone judge you by what you eat or drink, or with regard to a religious festival, a New Moon celebration or a Sabbath day. These are a shadow of the things that were to come; the reality, however, is found in Christ. (Colossians 2:16-17 [NIV])
These particular laws, inclusive of circumcision of the flesh, are all foreshadows that point to different realities found in the new covenant. Let me map it out for you:
1. Passover lamb requirement = Jesus Christ as the reality of the passover lamb.
2. Festival of Unleavened Bread = reality to put away sin.
3. Festival of First Fruits = reality of the resurrection of Jesus Christ.
4. Festival of Weeks (Pentecost) = reality of the giving forth of the holy spirit.
5. Festival of Trumpets = reality of the second coming of Jesus Christ with the sound of trumpets.
6. Day of Atonement = reality of the gathering of the elect from all over the world.
7. Festival of Booths = reality of the time the elect will begin to live in the encampment that will exist in Israel for them.
8. Seventh Day Sabbath = reality of the millennial kingdom of Jesus Christ that corresponds with the last thousand years of the full seven thousand years for this heaven and earth to exist.
9 Circumcision of the flesh = reality of the circumcision of the heart to discard your sinful nature (foreskin of the heart), and free you from sin.
10. Abstinence from foods = reality to not yoke together with unbelievers, for the behaviors of unclean animals symbolize the behaviors of ungodly men.
As such, these laws that are identified as shadows, are obeyed by fulfillfing their respective realities. Whereas laws, such as, "do not kill", "do not murder", still apply in their literal sense.