Elder D. Todd Christofferson recently posted on his Facebook page:
“Someone recently asked me why the Brethren are focused on teaching about Sabbath day observance throughout the world. The answer is very simple. It came as a direct revelation to the First Presidency and the Twelve from the Lord.
If we keep the Sabbath day holy, individuals will be stronger and will experience a transforming depth of spiritual maturity. The Lord has taught for centuries to let the Sabbath be a delight for all. We are all learning and teaching this law anew worldwide. We know it will bless all."
Remember the Sabbath day, to keep it holy (Exodus 20:8) echoes down to us from Mt. Sinai. The Lord is still speaking to us by the mouth of his holy prophets, which have been since the world began (Luke 1:70). Modern prophets, as anciently, are giving us the Lord's commandments and direction. This commandment, emphasized anew, is designed to bless us by focusing our Sabbath day on worshiping the Lord and refreshing us from our weekday labours.
See here and here for additional prophetic guidance on Sabbath day observance.