In addition to not being able to buy or sell unless you have the mark of the beast, at the very end, the deception will be so great, that almost the entire world will be deceived. A death decree will be setup for those that keep God’s commandments, including the Seventh Day Sabbath (Friday sundown to Saturday sundown):
And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.
Revelation 13:14,15
And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
This is because those that are deceived did not truly love God or the truth:
And for this cause God shall send them strong delusion, that they should believe a lie:
2 Thessalonians 2:11,12
That they all might be damned who believed not the truth, but had pleasure in unrighteousness.