Before the New Testament was even finished the early church had already begun to worship on the 1st day of the week in honor of the Resurrection of Our Lord Jesus Christ.
We ceased to be Jews by virtue of the New Testament and by having been thrown out of the temples and persecuted by the Jews & Romans.
Matthew 28:1
And in the end of the sabbath, when it began to dawn towards the first day of the week, came Mary Magdalen and the other Mary, to see the sepulchre.
Mark 16:2
And very early in the morning, the first day of the week, they come to the sepulchre, the sun being now risen.
Mark 16:9
But he rising early the first day of the week, appeared first to Mary Magdalen, out of whom he had cast seven devils.
Luke 24:1
And on the first day of the week, very early in the morning, they came to the sepulchre, bringing the spices which they had prepared.
John 20:1
And on the first day of the week, Mary Magdalen cometh early, when it was yet dark, unto the sepulchre; and she saw the stone taken away from the sepulchre.
These verses show that it was already the practice of the Early Church.
Acts Of Apostles 20:7
And on the first day of the week, when we were assembled to break bread, Paul discoursed with them, being to depart on the morrow: and he continued his speech until midnight.
1 Corinthians 16:2
On the first day of the week let every one of you put apart with himself, laying up what it shall well please him; that when I come, the collections be not then to be made.