Read the scriptures in the piece. There is not one verse that proves anything.
Doctrine isn't always easy.
This particular doctrine is easy. It's the 4th commandment, the 7th day sabbath was created by Christ and for Christ, and Christ kept the sabbath.
Luk 4:31 And came down to Capernaum, a city of Galilee, and taught them on the sabbath days.
Luk 4:32 And they were astonished at his doctrine: for his word was with power.