Wading in....
The lesson (doctrine) of the feast of the unleavened bread is for us to examine ourselves and purge (repent) of the sin (leaven) in our lives before we come to the cross (passover) and enter into salvation through Christ's righteousness.
As far as the new covenant instruction for the Christian, we need to esablish when the new covenant came into effect. A covenant is a contract between two parties. In this case between God and His people. Everything in that contract that is binding has to be there before the contract is signed, correct? Anything after that point cannot be considered to be part of the contract or covenant. Jesus shedding His blood was the seal or signature to that new covenant. Considering that there is zero scriptural backing for keeping the first day of the week before the cross, then we are bound by the teachings and commands up to that point.
John 14:15
If ye love me, keep my
commandments.
John 14:21
He that hath my
commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him.
John 15:10
If ye keep my
commandments, ye shall abide in my love; even as I have kept my Father's
commandments, and abide in his love.
Mark 2:28
Therefore the Son of man is Lord also of the
sabbath.
Mark 6:2
And when the
sabbath day was come, he began to teach in the synagogue:
Everything after that is just clarification and expansion on the teachings of the new covenant and has to be understood in that context.
The keeping of the first day of the week didn't start to be part of the early church until sometime between 100 and 200 AD. Do a brief history check to prove this point out.
Acts 13:42
And when the Jews were gone out of the synagogue, the Gentiles besought that these words might be preached to them the next
sabbath.
John the revelator would not have penned the words in Rev. 14 if keeping the commandments of Christ, which includes the 4th, were not still in effect some 70 years after the cross.
Revelation 14:12
Here is the patience of the saints: here are they that keep the
commandments of God, and the faith of Jesus.