How can God command circumcision as a perpetual institution, and then say henceforth men do not need to be circumcised?
How could God command the prescribed rituals of Passover as a perpetual intitution, and then drop the Old observance of Passover in the Christian era?
, How could God command The observance of the Seventh Day as The Sabbath, and then countenance the observance of Sunday as the Lord's Day?
The answers. Or at least one part, one aspect of the answer, because this goes very deep.
Circumcision was fulfilled and taken up into Baptism as the way to be initiated into God's community, and Passover was fulfilled and taken up into Easter (Pascha) as the celebration of our liberation from slavery, sin and death. Saturday marked the rest of God after He had worked for six days in Creation; Sunday marks the day of the Lord's Resurrection, His greatest work of all; the dawn of the New Creation.
The prohibition of consuming blood was because of the sacredness of life ( "Life is in the blood") and this was fulfilled by God's astounding invitation to us now not to refrsin, but to partake of the Sacred, in fact the most Sacred object in the visible Universe, the precious Blood of the Lamb, Our Lord Jesus Christ.
This is not the blood of a strangled chicken, which defiles. This is the saving, lifesaving Blood of God's dearly beloved Son, which purifies us and makes us clean.
The Old Covenant was the time of signs and symbols. The New Covenant is concealed in the Old; the Old Covenant is revealed in the New. This is the perennial Faith of the Church. Then, for 2,000 years, and now: we proclaim the death of the Lord, and profess His Resurrection, until He comes again.