"It may seem to some that the mere question of whether we shall 
observe one day of the week or another is so small a matter to serve as the only great test of man’s loyalty to God, but as the final preparation for the coming of the Lord.
So it would be if it was merely a question of days.
But:
It is a question of loyalty to God’s Word, and therefore of loyalty to God Himself.
It is a question of whether
men will regard God as supreme,
and His Word as expressing
completely His will,
or whether they will
divide honors with a rival power.
It is a question of whether men will strictly follow the example of Christ, or whether they will follow “the church” which presumes to know the will of God better than He did.
Remember this also: The same Word that says,
Exodus 20:10 The seventh day is the Sabbath of the Lord your God; in it you shall not do any work,...." E.J. Waggoner