The Sabbath Was Never Changed to Sunday
There is not a single verse in the Bible that says that the Sabbath was changed to Sunday.
Quite the opposite:
There remaineth therefore a rest [Sabbath-rest] to the people of God.
- Hebrews 4:9 (KJV)
In fact, why would a never-changing God, change His own laws? That doesn't make any sense.
We must then make a choice, e.g. obedience (Sabbath) or disobedience (Sunday).
If the light of truth has been presented to you, revealing the Sabbath of the fourth commandment, and showing that there is no foundation in the word of God for Sunday observance, and yet you still cling to the false Sabbath, refusing to keep holy the Sabbath which God calls "My holy day," you receive the mark of the beast. When does this take place?-When you obey the decree that commands you to cease from labor on Sunday and worship God, while you know that there is not a word in the Bible showing Sunday to be other than a common working-day, you consent to receive the mark of the beast, and refuse the seal of God. If we receive this mark in our foreheads or in our hands, the judgments pronounced against the disobedient must fall upon us. But the seal of the living God is placed upon those who conscientiously keep the Sabbath of the Lord.
- Ellen White, The Review and Herald, July 13, 1897, par. 6