Genesis 1:3 And God said, Let there be light: and there was light. 4 And God saw the light, that it was good: and God divided the light from the darkness. 5 And God called the light Day, and the darkness he called Night. And the evening and the morning were
the first day.
Genesis 2:1 Thus the heavens and the earth were finished, and all the host of them. 2 And
on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. 3 And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.
God began creation on the first day (Sunday), and rested on the last day (Saturday, the Sabbath). So every week begins with a Sunday, and ends with a Saturday. That's the established pattern. Of course, most modern Western business weeks begin Monday morning, and end Friday afternoon, so they have a 5-day work week.
Jesus arose on Resurrection
Sunday, the day after the Sabbath (Saturday).
Matthew 28:1
In the end of the sabbath, as it began to dawn toward the first day of the week, came Mary Magdalene and the other Mary to see the sepulchre.
Mark 16: 1 And when
the sabbath was past, Mary Magdalene, and Mary the mother of James, and Salome, had bought sweet spices, that they might come and anoint him. 2 And very early in the morning
the first day of the week, they came unto the sepulchre at the rising of the sun.
Mark 16:9 Now when Jesus was risen early
the first day of the week, he appeared first to Mary Magdalene, out of whom he had cast seven devils.
Luke 24:1 Now upon
the first day of the week, very early in the morning, they came unto the sepulchre, bringing the spices which they had prepared, and certain others with them.
John 20:1
The first day of the week cometh Mary Magdalene early, when it was yet dark, unto the sepulchre, and seeth the stone taken away from the sepulchre.
John 20:19 Then the same day at evening, being
the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you.