It is common for Muslim teachers to claim they are better Christians than Christians, because they follow the path of Jesus. Since Jesus was born under the Law as a Jew, he did follow the law of Moses and fulfill it.
The problem is Jesus removed the law through his death. The Muslims use the following to claim superiority over Christians.
Circumcision
Not eating pork
head coverings
keeping the torah
This isn't a complete list. It is enough to show Islam doesn't practice Christianity or keep the law. They aren't good Christians, much less better Christians. None of these above are commanded in Christianity.
First, Abraham wasn't justified by circumcision. Abraham was justified in Genesis 15 two chapters before God gave circumcision. The practice was a remembrance of the faith he had before circumcised. The Christians living with Jesus (James) and those who were Apostles taught by Jesus, said in Acts 15, circumcision wasn't required. They claim to be better Christians than Peter and James.
Circumcision was required for the physical family of Abraham and established a physical identity, seeing it as a remembrance of past faith was for spiritual people. Muslims are therefore carnal and not using circumcision correctly. In this sense Muslims aren't the spiritual children of Abraham. Circumcision did not act in his justification. Even the offering of Isaac was apart from circumcision. It was separate from the ordinance.
Circumcision was never a command for non-Abrahemic peoples, therefore blanket statements over all Christians are theologically immature.
Requiring circumcision for justification is not following Jesus or being a good Christian. Jesus was circumcised by parents, not by his will and not for justification. Jesus admitted baptism was necessary to "fulfill all righteousness", so his circumcision and law keeping could not justify on its own. Justification requires the righteousness of faith. Islam sees righteousness thru submission to law, not faith in promise. James 2 portrays obedience of faith, not obedience of submission. We submit to Christ thru faith.
Realize Abraham's righteousness was "imputed" and not earned through legal constant obedience.
Genesis 15:6
and he believed in the Lord and it was counted to him for righteousness
James 2:23
And the scripture was fulfilled which saith, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God.
Realize Jesus never taught a lesson on circumcision in the gospels. He mentioned circumcision once in a dispute over the sabboth day and types of works. It is hypocrisy that Muslims only hear Jesus and not the Apostles, but Jesus never commanded circumcision or taught a direct message on it.
John 7:21
Jesus answered and said unto them, I have done one work, and ye all marvel.
John 7:22
Moses therefore gave unto you circumcision; (not because it is of Moses, but of the fathers;) and ye on the sabbath day circumcise a man.
John 7:23
If a man on the sabbath day receive circumcision, that the law of Moses should not be broken; are ye angry at me, because I have made a man every whit whole on the sabbath day?
Jesus admits it is only the Law of Moses that is broken, and only those under the law could violate it. Then he says the man was made "every whit whole", he was as whole as if keeping the law.
The jews were mutilating foreskins while Jesus was healing, both works done on the body. Jews allowed one and not the other. Jews would circumcise on the sabboth if the 8th day fell on it, but would not heal the body if it fell on the 8th day. Hypocrites in application. Since Jesus' focus was healing vs circumcising, he did not consider that work important to his ministry. It was important to physical Israel as a remembrance.
Muslims aren't better Christians, but better Pharisees. They think the power is in the physical act of circumcision and obedience vs the remembrance of Abraham's justification, which was before the law and before circumcision, this remembrance memorialized continued faith.
All of the above are liberties. One may keep the Torah except if claiming it saves us.
We are no longer under the Torah except for learning history and prophecy. The scriptures give us a lot that we can use, but not as a law. We are under the law of Christ. The scriptures of the old testament give us background information.
Romans 15:4
For whatsoever things were written aforetime were written for our learning, that we through patience and comfort of the scriptures might have hope.
The law of itself without faith in Jesus Christ can't save mankind. It can condemn but can't save.
2 Timothy 3:15
And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus.