More fully keep thyself unspotted from the world

Doctrine and Covenants 59:9

And that thou mayest more fully keep thyself unspotted from the world, thou shalt go to the house of prayer and offer up thy sacraments upon my holy day; https://www.lds.org/scriptures/dc-testament/dc/59?lang=eng

The Sabbath is one of the most important commandments in the entire gospel plan