In the context of “spiritual circumcision” I don't think God cares what language you call his name in, or what day you wish to set aside as his day, or even if you want to decorate a Christmas tree; so long as you do it in the right spirit, and ask for forgiveness in his name.
I believe the majority of Christian theologians agree with me on this point. They railed against injustices committed in the name of our lord, and the fallen nature of our world, most could give a fig for what day the Sabbath was observed on; and they certainly knew the Sabbath wasn't on Sunday.
That may be a common understanding today, but it's not really supported by scripture. It's not really what Paul was talking about when he spoke of "circumcision of the heart.".
Rom 2:27 And shall not uncircumcision which is by nature, if it fulfill the law, judge thee, who by the letter and circumcision dost transgress the law?
Rom 2:28 For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh:
Rom 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
Paul was referring specifically to assertions by Jews (by Christian Jews and non-Christians) that one had to be circumcised physically in order to share in the new covenant. Of course this was not correct since God had granted his holy spirit to non-circumcised gentiles.
Paul's point was that outward observation means nothing without an inward obedience to the holy spirit:
Rom 2:21 you, therefore, who teach another, do you not teach yourself? You who preach that one shall not steal, do you steal?
Rom 2:22 You who say that one should not commit adultery, do you commit adultery? You who abhor idols, do you rob temples?
Rom 2:23 You who boast in the Law, through your breaking the Law, do you dishonor God?
In other words, the lesson Paul was teaching about circumcision of the heart is that we shouldn't be hypocritical. Our outward actions should match the inward expression of the spirit of the Lord.
I believe the majority of Christian theologians agree with me on this point. They railed against injustices committed in the name of our lord, and the fallen nature of our world, most could give a fig for what day the Sabbath was observed on; and they certainly knew the Sabbath wasn't on Sunday.
I don't doubt that many modern theologians would agree. This is mostly due to time and tradition though. In the case of the sabbath, Jesus Christ created the sabbath holy. He observed it while in the flesh because not to so would have been a sin, a violation of his, Gods' laws. He still wishes to observe it while his spirit resides in us. He still does not want to sin. If we don't exert our will and follow his will, we will keep the sabbath because it his desire, not ours.