I don't confess to understand the mark completely, but here is what I think in part. We are not to buy and sell or work on the Sabbath day as shown in:
Nehemiah 10:31: "And if the people of the land bring ware or any victuals on the Sabbath day to sell, that we would not buy it of them on the Sabbath, or on the holy day..."
Nehemiah 13:15-21: "In those days saw I in Judah some treading wine presses on the sabbath, and bringing in sheaves, and lading asses; as also wine, grapes, and figs, and all manner of burdens, which they brought into Jerusalem on the sabbath day: and I testified against them in the day wherein they sold victuals. There dwelt men of Tyre also therein, which brought fish, and all manner of ware, and sold on the sabbath unto the children of Judah, and in Jerusalem. Then I contended with the nobles of Judah, and said unto them, What evil thing is this that ye do, and profane the sabbath day? Did not your fathers thus, and did not our God bring all this evil upon us, and upon this city? yet ye bring more wrath upon Israel by profaning the sabbath. And it came to pass, that when the gates of Jerusalem began to be dark before the sabbath, I commanded that the gates should be shut, and charged that they should not be opened till after the sabbath: and some of my servants set I at the gates, that there should no burden be brought in on the sabbath day. So the merchants and sellers of all kind of ware lodged without Jerusalem once or twice. Then I testified against them, and said unto them, Why lodge ye about the wall? if ye do so again, I will lay hands on you. From that time forth came they no more on the Sabbath."
So the mark given by the Beast allows people to buy and sell, but those who don't take the mark cannot buy and sell. The reason they cannot buy and sell is because they honor the Sabbath day (not Sunday, but the 7th day Sabbath which falls on Saturday) so they cannot buy and sell. Those who do not honor the true Sabbath therefore can buy and sell on the true Sabbath because they think Sunday is the true Sabbath. I do not think this is a literal mark, but rather a spiritual mark. Your master is determined by the day you think is the Sabbath. As for me, I will honor the 7th day, not the 1st day of the week. The only way it becomes a literal reality is when a Sunday law is instituted and worship becomes mandatory on that day, those who obey are therefore spiritually marked. Those who currently worship on Sunday won't even care when it is made a law because it won't effect them in the least.