Mark 2:27–28: Was the Sabbath Made for Man?
Jesus does not set the Sabbath aside in Mark 2:27–28. He relocates its purpose to the good God intended for people, then claims lordship over the day himself.
Acts 20:7: Does Sunday Worship Break a Command?
Acts 20:7 describes a real gathering of disciples on the first day of the week, with Paul teaching before his departure. It reports what happened, and reporting is not the same as commanding, so the verse neither legislates Sunday nor makes it a sin.